@aquaVen
Wow, man, I'm really sorry. Things just seem to be going from bad to worse for you. Just remember that things generally get worse before they get better, and I must say that your courage in this situation is admirable.
To answer your question about whether or not people are born that way:
So far, to my knowledge, there isn't any proof that it is genetic. Most of the test that I come across say that the results are inconclusive, so I take that to mean that they are still searching for it.
While I don't believe that it is genetic (whether normality or abnormality), I do believe that people can be "born" gay, in the sense that they have a general leaning towards it. As I've said, as a Christian, I believe that each person has a particular sin that they struggle with, with homosexuality being a sin under the Christian religion. That isn't to say that there aren't influences outside. I also believe that some who are homosexuality did, in fact, choose it based on influences from their environment.
Let me be absolutely clear, I do not believe that homosexuality is acceptable behavior. I am not saying that just because a person's tendencies cause them to feel and think that it is okay, then the action is perfectly fine. You probably already know this, but God doesn't call temptation a sin, so being tempted by something is perfectly normal in Christianity.
I can't really say anything about his engagement, so I won't. However, I've always felt that people should be able to accept others feelings about life, religion, ect. So, even though you should definitely consider his feelings, I don't think it would be bad of you to talk to him about how you feel regarding the situation.
Again, I wish you the best of luck in this, and I pray that your family regains its stability soon.