He has repented from not praying and fasting; does he have to make up what he missed?

Firstly: 

We praise Allaah for having blessed you with guidance, and we
ask Him to increase you in knowledge and guidance. We remind you to give
thanks to Allaah for this great blessing, for gratefulness increases the
blessing. Allaah says (interpretation of the meaning): 

“And (remember) when your Lord proclaimed: If you give
thanks (by accepting Faith and worshipping none but Allaah), I will give you
more (of My Blessings); but if you are thankless (i.e. disbelievers),
verily, My punishment is indeed severe”

[Ibraaheem 14:7]

Secondly: 

What you have mentioned about the conditions of repentance is
correct. With regard to making up missed acts of worship such as prayer and
fasting, there are two opinions among the scholars. Some of them say that
they must be made up, and this is the view of the majority.  

Some scholars say that the one who did not pray does not have
to make up the prayers that he missed, based on the view that he was a
kaafir (when he did not pray). Hence his repentance is his becoming Muslim,
which erases all the sins that came before it. 

Some of the scholars do not think that the one who did not
pray deliberately has to make it up, whether they think that he was a kaafir
or otherwise, because the text only speaks of those who have excuses, such
as the one who sleeps and misses a prayer or forgets it. 

What is indicated by the saheeh evidence is that the one who
does not pray is a kaafir, whether he does not pray because of laziness or
denial that prayer is obligatory. See the evidence for that in question no.
5208. 

Obliging the penitent to make up the prayers he has missed
makes repentance too difficult, and puts people off. But the penitent should
do a lot of good deeds, because Allaah says (interpretation of the
meaning): 

“And verily, I am indeed forgiving to him who repents,
believes (in My Oneness, and associates none in worship with Me) and does
righteous good deeds, and then remains constant in doing them (till his
death)”

[Ta-Ha 20:82]

The Standing Committee for Issuing Fatwas was asked: I went
to the United States to study and I spent five years there, during which I
did not pray or fast. Allaah has guided me and I have become righteous,
praise be to Allaah. How can I make up these prayers and fasts? 

They replied: 

If the situation is as you describe, and you have repented
and begun to follow the way of guidance, you do not have to make up the
prayers and fasts that you deliberately did not do, because not praying is
major kufr and apostasy from Islam, even if the one who does not pray does
not deny that it is obligatory. This is according to the more sound of the
two scholarly opinions. If the apostate becomes Muslim again, he is not
enjoined to make up the prayers and fasts that he missed during his
apostasy, because the Prophet (peace and blessings of Allaah be upon
him) said: “Islam erases that which came before it, and repentance erases
that which came before it.”  But in the future you have to pray regularly in
congregation and on time with the Muslims in the mosque, and observe the
Ramadaan fast. It is also prescribed for you to do a great deal of good
deeds and naafil acts of worship such as prayer, fasting, upholding ties of
kinship, giving charity and other good deeds, as much as you can, because
Allaah says (interpretation of the meaning): 

“And verily, I am indeed forgiving to him who repents,
believes (in My Oneness, and associates none in worship with Me) and does
righteous good deeds, and then remains constant in doing them (till his
death)”

[Ta-Ha 20:82

We ask Allaah to make us and you steadfast in adhering to the
truth and following the right path. 

End quote from Fataawa al-Lajnah al-Daa’imah (6/41). 

See also question no. 610. 

Thirdly: 

With regard to the girl, you should cut off all ties with
her, so that the shaytaan will not find a way to tempt you to go back to a
relationship with her. If you can find some righteous women who can call her
to Islam, that is good. 

We ask Allaah to increase you in steadfastness. 

And Allaah knows best.