Praise be to Allaah.
Homosexuality is a major sin which deserves the most severe
of punishments in this world and in the Hereafter. See Question no.
5177. But the person who does that cannot be
described as a kaafir because of that, unless he thinks that it is
permissible and claims that it is halaal – in which he is to be denounced as
a kaafir. But simply doing it whilst admitting that it is haraam does not
put a Muslim beyond the pale of Islam. He is still a Muslim, but he is
exposed to the wrath of Allaah and is committing a major sin. It is not
permissible for you to go ahead and marry him until he repents sincerely.
Simply promising does not count as repentance. My advice to you is not to go
ahead and marry him, rather you have to look for a righteous man who will be
the means of bringing you happiness in this world and in the Hereafter.
Homosexuality, just like other major sins, is open to repentance: whoever
repents, Allaah will accept his repentance.