He is very distressed because of his father’s dealing in riba (usury)

Riba (usury) is a grave sin which the
Muslim is obliged and required to avoid. 

Allah, may He be exalted, says
(interpretation of the meaning):

“O you who believe! Fear Allah and give
up what remains (due to you) from Ribaa (from now onward) if you are
(really) believers.

279. And if you do not do it, then take
a notice of war from Allah and His Messenger but if you repent, you shall
have your capital sums. Deal not unjustly (by asking more than your capital
sums), and you shall not be dealt with unjustly (by receiving less than your
capital sums)”

[al-Baqarah 2:278-279]. 

It was narrated that Jaabir said: The
Messenger of Allah (peace and blessings of Allah be upon him) cursed the one
who consumes riba and the one who pays it, the one who writes it down and
the two who witness it, and he said: they are all the same.

Narrated by Muslim (1598). 

When a person takes out a riba-based loan,
the only one who sins is the one who does it; there is no sin on his family,
unless they approve of that or help him. But if they object to his action
and advise him not to do it, then there is no sin on them, because they have
not done anything haraam. 

Allah, may He be exalted, says
(interpretation of the meaning):

“and no bearer of burdens shall bear
the burden of another. Then unto your Lord is your return, so He will tell
you that wherein you have been differing”

[al-An‘aam 6:164]

“And no bearer of burdens shall bear
another’s burden, and if one heavily laden calls another to (bear) his load,
nothing of it will be lifted even though he be near of kin. You (O Muhammad
(blessings and peace of Allah be upon him)) can warn only those who fear
their Lord unseen, and perform As-Salat (Iqamat-as-Salat). And he who
purifies himself (from all kinds of sins), then he purifies only for the
benefit of his ownself. And to Allah is the (final) Return (of all)”

[Faatir 35:18]. 

Shaykh ‘Abd ar-Rahmaan as-Sa‘di (may Allah
have mercy on him) said: 

The words “And no bearer of burdens
shall bear another’s burden” mean: on the Day of Resurrection, each one
will be requited for his deeds, and no one will bear the burden of sin of
anyone else. “and if one heavily laden calls another to (bear) his load”
means: if a soul that is heavily laden with sins and transgressions seeks
help from someone else to take some of his burden, “nothing of it will be
lifted even though he be near of kin” because no burden can be taken
from a relative. End quote from Tayseer al-Kareem ar-Rahmaan fi Tafseer
Kalaam al-Mannaan (p. 687) 

Your distress or sorrow at the sin of your
father is something praiseworthy and indicates that your heart is
spiritually alive and fears Allah, may He be exalted, but if this distress
reaches the level of thinking of suicide, then it becomes blameworthy,
because it has ceased to be useful and has become harmful. Hence you must
strive to overcome it and focus on doing righteous deeds. 

Shaykh al-Islam Ibn Taymiyah (may Allah
have mercy on him) said: 

As for distress or grief, it is not
enjoined by Allah or His Messenger; rather it is prohibited in several
places, even if it has to do with matters of religion, as in the verses in
which Allah, may He be exalted, says (interpretation of the meaning):

“So do not become weak (against your
enemy), nor be sad, and you will be superior (in victory) if you are indeed
(true) believers”

[Aal ‘Imraan 3:139]

“And grieve not over them (polytheists
and pagans, etc.), and be not distressed because of what they plot”

[al-Nahl 16:127]

“and he (blessings and peace of Allah
be upon him) said to his companion (Abu Bakr ): “Be not sad (or afraid),
surely Allah is with us”

[at-Tawbah 9:40]

“And let not their speech grieve you (O
Muhammad (blessings and peace of Allah be upon him))”

[Yoonus 10:65]

“In order that you may not be sad over
matters that you fail to get, nor rejoice because of that which has been
given to you”

[al-Hadeed 57:23].

And there are many similar examples. 

That is because it does not bring any
benefit or ward off any harm, so it does not serve any purpose, and whatever
does not serve any purpose, Allah does not enjoin it. 

Grief or sorrow may be an indication of
something for which a person will be rewarded and praised, so it is
praiseworthy in that sense; it is not praiseworthy in and of itself, as in
the case of one who is grieved by a calamity that affects his religious
commitment, or is grieved by calamities that befall the Muslims in general.
Such a person will be rewarded for what is in his heart of love for good and
hatred of evil, and the like. 

But if it leads to discouragement and
being distracted from doing that which Allah and His Messenger have
enjoined, then it is blameworthy in this regard, even if it is praiseworthy
in some other aspects. End quote.

Majmoo‘ al-Fataawa
(10/16-17) 

Ibn al-Qayyim (may Allah have mercy on
him) said: 

The Prophet (blessings and peace of Allah
be upon him) regarded grief as something from which one should seek refuge
with Allah, because grief leads to discouragement, weakens resolve and
undermines willpower. There is nothing more beloved to the Shaytaan than the
grief of the believer. Allah, may He be exalted, says (interpretation of the
meaning):

“Secret counsels (conspiracies) are
only from Shaytaan (Satan), in order that he may cause grief to the
believers”

[al-Mujaadilah 58:10]. 

Grief is one of the diseases of the heart
(spiritual diseases) that prevent a person from recovering and striving hard
… But grief may be praiseworthy in terms of its cause, source or
implications, not in and of itself. The believer may feel grief for his
carelessness and shortcomings in serving and worshipping his Lord, or he may
feel grief for going to extremes in opposition, disobedience and wasting his
time. This is indicative of the soundness of the faith in his heart and of
his spiritual wellbeing , because his heart feels such pain, hence he feels
grief. But if his heart is dead (spiritually deadened), he will not feel
that and he will not feel any grief or sorrow, because the dead do not feel
the pain of wounds. The more spiritually alive his heart is, the more he
will feel this pain. But grief does not help at all, because it leads to
discouragement, as mentioned above. Rather what benefits the heart is to
focus the mind, strive hard, roll up one sleeves and do one’s utmost. End
quote.

Tareeq al-Hijratayn
(2/607-608) 

Secondly: 

The grief that you are feeling, that has
led you to think of suicide, is something unwise. The wise person would not
commit a grave sin due to sorrow for the sin of someone else. Suicide is not
an insignificant sin. 

It was narrated from Abu Hurayrah (may
Allah be pleased with him) that the Prophet (blessings and peace of Allah be
upon him) said: “Whoever throws himself down from a mountain and kills
himself will be in the Fire of Hell, throwing himself down in it for ever
and ever. Whoever drinks poison and kills himself will be in the Fire of
Hell, sipping it for ever and ever. Whoever kills himself with a piece of
iron will have that iron in his hand, thrusting it into his belly in the
Fire of Hell for ever and ever.”

Narrated by al-Bukhaari (5778) and Muslim
(109). 

Rather you have to understand that no
matter what has befallen you of worry and grief, whether that is because of
your father’s debts and sin, if you bear it with patience and seek reward
for that with Allah, may He be exalted, and you hasten to set straight
whatever you can, then it you will be among those who are forgiven. 

It was narrated from Abu Sa‘eed al-Khudri
and Abu Hurayrah (may Allah be pleased with them both) that the Prophet
(blessings and peace of Allah be upon him) said: “No hardship, pain, worry,
grief, harm or distress befalls a believer – not even a thorn that pricks
him – but Allah will expiate some of his sins thereby.”

Narrated by al-Bukhaari (5642) and Muslim
(2573). 

Thus you may attain triumph by meeting
Allah, may He be exalted, with no sin on you.

It was narrated that Abu Hurayrah (may
Allah be pleased with him) said: The Messenger of Allah (blessings and peace
of Allah be upon him) said: “Calamity will continue to befall the believing
man and woman with regard to themselves, their children and their wealth,
until the believer will meet Allah with no sin on him.”

Narrated by at-Tirmidhi (2399). He said:
This is a hasan saheeh hadeeth. It was also classed as saheeh by al-Albaani
in Silsilat al-Ahaadeeth as-Saheehah (2280) 

You have to offer a lot of supplication,
calling upon Allah, may He be exalted, sincerely, especially at the times
when supplications are answered, such as the last third of the night, and
when prostrating in prayer. You must also cast aside the despair in your
heart, and be optimistic and have certain faith that Allah is able to do all
things, and is Most Merciful towards His creation, for you do not know when
relief will come. 

Allah, may He be exalted, says, telling us
of the advice that Ya‘qoob (peace be upon him) gave to his sons
(interpretation of the meaning):

“and never give up hope of Allah’s
Mercy. Certainly no one despairs of Allah’s Mercy, except the people who
disbelieve”

[Yoosuf 12:87]. 

Shaykh ‘Abd ar-Rahmaan as-Sa‘di (may Allah
have mercy on him) said:

“and never give up hope of Allah’s
Mercy”, for hope requires the individual to strive hard for what he
hopes for, whereas despair makes him lethargic and apathetic. The best thing
that people may hope for is the grace, kindness, mercy and compassion of
Allah. “Certainly no one despairs of Allah’s Mercy, except the people who
disbelieve”, for as a result of their disbelief they think it unlikely
that He will have mercy on them, so His mercy is far removed from them; so
do not be like the disbelievers. 

This indicates that a person’s hope of the
mercy and grace of Allah will be commensurate with the level of his faith.
End quote.

Tayseer al-Kareem ar-Rahmaan fi Tafseer
Kalaam al-Mannaan (p.
404) 

To sum up:

You are not to blame so long as you
objected to what your father was doing and tried to advise him. Rather Allah
may reward you for what you do of giving advice. But you have to strive hard
to do righteous deeds and do not be a prisoner to your grief, for grief
opens a door to the Shaytaan, who will try to make you despair of the mercy
of Allah, may He be exalted, and refrain from doing good deeds and hastening
to do them. You have to carry on trying to advise your father and striving
hard in supplication for him. 

We ask Allah, may He be exalted, to
relieve you of your worry and grief, and to guide your father. 

And Allah knows best.