Ankush puttar, the situation is a little bit tricky. But rather common too, in any kind of relationship. Though things are sailing very smoothly, one person is scared of the future storms and refuses to anchor down. I know that you want this to work out but remember, a relationship is a two person game. You can't want what the other person wants. That can't lead to anything good or long term.
Hostile environment
So, you boys have been together for three years now. Great going ji, this is definitely much more than many young people can claim to have. That also means that there is something real that has kept you together.
So I am assuming that the problem is that he can't commit to any man, not just you. Ankush betaji, your first conversation with him should be to clarify this. It's not you, it’s your gender.
I am sure that you already know him well, but maybe try to understand your boyfriend's anxieties. In India, we still don't respect non-traditional relationships the way we ought to. You kids must face a mixture of judgment, contempt and jealousy. I can imagine that it cannot be easy living in such a hostile environment. And though the things are getting better, it'll take a lot longer for things to normalise.
Pressure
Puttar ji, bisexual or not, the matter is of wanting the same things in life. As it appears, you want a long-term relationship with the other ma da ladla and a house, life, family, or whatever else rocks your nauka together. But he likes the heterosexual ‘settling down’ idea and wants to be with a girl in the long term.
You can talk to him and probe if it is just societal pressure, or if it’s what he really wants.
If it is only about outside pressure, then he could decide to find support from you and other friends, and tell his parents and family about it – after he is standing on his own two feet (important to have financial independence before risking a clash, ji).
Cut your losses
But otherwise, I will have to give you the tough advice of cutting your losses and breaking up. There is no point in investing in a relationship that'll go nowhere. Save your emotions for someone better. I know it'll hurt a lot. But if your boyfriend wouldn't even consider changing his mind, I don't see any point in hanging to the threadbare hope.
If he really wants to be with some nice girl then you should take stock of your future and find a better life. It is very distressing to lose a first love and you should also have support through this phase. I am here, but also discuss and be with close friends who can pull you through.
Trust and truth
What will happen if your boyfriend does marry a girl and you two have still not made the break? Will he tell her about you? Perhaps he will find it too hard to stop seeing you and try to keep both relationships going. You and the girl could both end up with a broken heart.
I have no problem with polyamory but as long as everyone in the relationship knows what is going on. Pati, patni aur woh, all should play by same rules. Hetero, homo, bi, or any other you like, trust and truth are very, very important ji, whether it’s love, sex or roka! (Matlab shaddi waddi, you know what I mean!)
You deserve better
I also had a situation similar to yours. You know the first boy I ever kissed totally broke my heart by telling me that he is into boys. To this day I wonder if I really kissed that badly! It took me time, but eventually I came to terms with the situation. But then, my English textbook said that all’s well that ends well. After only a few such incidents, I finally found your Malhotra Uncle. And we complete 40 glorious years together this 6th of July.
Whatever happens ji, please don’t beat yourself up over this. It’s not your fault, I am sure you are a fabulous person and deserve someone who loves and cares for you just the way you do. Ishaq di gaddi nu one way te nahi le jande. Khus raho te abaad raho, roohaza piyo, aur Auntyji ko pado.