The believer’s family joining him in Paradise

Firstly, you say, “does this include those whom we loved but could not marry?”

The answer to this is that it is not permissible for a Muslim man to form a relationship with a non-mahram women, or for a Muslim woman to form a relationship with a man or to have an emotional attachment to him, except for her husband. See Questions nos. 9465, 5445, 1200.

Secondly, you say, “Will the people who go to Heaven be reunited with their loved ones who go to Hell?”

The answer is, yes, the people of Paradise will be reunited with their loved ones who went to Hell, if they were believers in Tawheed (the oneness of Allah). That will be by virtue of their intercession for them to be brought forth from Hell and admitted to Paradise. The evidence for that was narrated by al-Bukhaari in Kitaab al-Tawheed, no. 7440:

It was narrated that Abu Sa’eed al-Khudri said: “We said, ‘O Messenger of Allah! Shall we see our Lord on the Day of Resurrection?’ He said, ‘Do you have any difficulty in seeing the sun and the moon when the sky is clear?’ We said, ‘No.’ He said, ‘So you will have no difficulty in seeing your Lord on that Day, just as you have no difficulty in seeing the sun and the moon (in a clear sky). …Then the bridge will be laid across Hell.’ We said, “O Messenger of Allah! What is the bridge?’ He said, ‘It is a slippery (bridge) on which there are clamps and (hooks like) thorns which are wide at one side and narrow at the other and have bent ends. A plant with such thorns is found in Najd and is called al-Sa’daan. Some of the believers will cross the bridge as quickly as the wink of an eye, some others as quick as lightning, a strong wind, or fast horses or she-camels. So some will be safe without any harm; some will be safe after receiving some scratches, and some will fall down into Hell (Fire). The last person will cross by being dragged (over the bridge). You (Muslims) cannot be more pressing in claiming from me a right that has been clearly proved to be yours than the believers in interceding with Almighty Allah for their (Muslim) brothers on that Day, when they see themselves safe.

They will say, “O Allah! (Save) our brothers (for they) used to pray with us, fast with us and also do good deeds with us.” Allah will say, “Go and take out (of Hell) anyone in whose heart you find faith equal to the weight of one (gold) Dinar.” Allah will forbid the Fire to burn the faces of those sinners. They will go to them and find some of them in Hell (Fire) up to their feet, and some up to the middle of their legs. So they will take out those whom they will recognize and then they will return, and Allah will say (to them), “Go and take out (of Hell) anyone in whose heart you find faith equal to the weight of one half Dinar.” They will take out whomever they will recognize and return, and then Allah will say, “Go and take out (of Hell) anyone in whose heart you find faith equal to the weight of an atom (or a small ant),” and so they will take out all those whom they will recognize.’” Abu Sa’eed said, “If you do not believe me, read, if you wish, ‘Surely, Allah wrongs not even of the weight of an atom (or a small ant), but if there is any good (done), He doubles it…’ [al-Nisaa’ 4:40 – interpretation of the meaning].” The Prophet (peace and blessings of Allah be upon him) said: “Then the Prophets and Angels and the believers will intercede, and (last of all) the Almighty (Allah) will say, ‘Now remains My Intercession. He will then hold a handful of the Fire from which He will take out some people whose bodies have been burnt, and they will be thrown into a river at the entrance of Paradise, called the water of life. They will grow on its banks, as a seed carried by the torrent grows…”

But for those who believed in shirk, no intercession will benefit them. Allah says (interpretation of the meaning):

“Verily, Allah forgives not that partners should be set up with Him (in worship), but He forgives except that (anything else) to whom He wills”

[al-Nisaa’ 4:48]

Note that intercession is of two types:

“The first type is the kind of intercession that is the exclusive preserve of the Messenger (peace and blessings of Allah be upon him), which is of varying kinds, the greatest of which is the Great Intercession in the Station of praise and glory (al-maqaam al-mahmood) which Allah has promised to him in the aayah (interpretation of the meaning):

‘And in some parts of the night (also) offer the Salaah (prayer) with it (i.e. recite the Qur’aan in the prayer) as an additional prayer (Tahajjud optional prayer Nawaafil) for you (O Muhammad). It may be that your Lord will raise you to Maqaam Mahmood (a station of praise and glory, i.e., the honour of intercession on the Day of Resurrection)’

[al-Israa’ 17:79]

This intercession means that he will intercede for the people who are standing on the Day of Resurrection, so that the distress they are suffering will be reduced for them.

The second type is general intercession on the part of the Messenger (peace and blessings of Allah be upon him) for all the believers. This is of various kinds:

(i)Intercession for those who deserve Hell, so that they will not enter it. This is indicated by the words of the Messenger (peace and blessings of Allah be upon him), “There is no Muslim who dies and forty men who do not associate anything with Allah pray the funeral prayer for him, but Allah will accept their intercession for him.” (narrated by Muslim, 2/655).

(ii)Intercession for those who have entered Hell, so that they will be brought forth from it. It was narrated that Abu Sa’eed al-Khudri said: “The Messenger of Allah (peace and blessings of Allah be upon him) said: ‘By the One in Whose hand is my soul,

You (Muslims) cannot be more pressing in claiming from me a right that has been clearly proved to be yours than the believers in interceding with the Almighty for their (Muslim) brothers on that Day, when they see themselves safe.

They will say, “O Allah! (Save) our brothers (for they) used to pray with us, fast with us and also do good deeds with us.” Allah will say, “Go and take out (of Hell) everyone whom you recognize.” Allah will forbid the Fire to burn the faces of those sinners. So they will bring forth many people who were  in the Fire up to their calves or their knees.” (Narrated by Muslim,269)

(iii)Intercession to raise the believers in status. This is because of the du’aa’s of the believers for one another, as the Prophet (peace and blessings of Allah be upon him) said, making du’aa’ for Abu Salamah: “O Allah, forgive Abu Salamah, raise him in status among those who are guided, make his grave spacious for him and fill it with light, and protect his family who are left behind.” And there is the du’aa’ for intercession as the Prophet (peace and blessings of Allah be upon him) said: “There is no Muslim who dies and forty men who do not associate anything with Allah pray the funeral prayer for him, but Allah will accept their intercession for him.”

Reference: al-Qawl al-Mufeed, vol. 1, p. 332