Is it normal that my best friends are living together?

I have 2 close friends, yes we are all gay. We are older people (over 40). My one friend is a bit of a selfish idiot and he has discovered he is bipolar but he performs pretty normally everyday. My other friend is someone who's pretty giving but I feel he gets used a lot and is blind to it. I have tried to help him see our other friend is using him but now he moved in with him thinking he needs help. He has been living there for over a year. He has his own home and tenants living there. I don't know why he can't check in on the person and stay in his home that he is paying a mortgage on. Is this living situation normal?