How can I get back together with her?

I have a group of friends in class and we were just fine until one of my bestfriend named “A” suddenly become lonely person and wont join our conversation and sit behind and sleep. I know shes tired of her life coz her mom runaway from home and now she live with her dad and sis. And now she lost her laugh.. and now I feel like my relationship between me and A become colder and all we talk about is only serious thing about homework..i try many things to make her laugh..I even try to make a fool of myself by doing stupid jokes but she only smile..but I saw she was laughing with her other friend and not with me..yes.. I did feel jealous there..

And my “B” friend try to save me from A who she believe that A didn’t know how to appreciate friendship. B ignore A. so A feel left out and didn’t want to talk to B since she already did say Hello to B but B still ignore A..B wanted to teach A with that way with a reason that B wont forgive A mistake until she say sorry to me..

But from my perspective point of view.. the reason she cant laugh with me is because B was nice to me but not to her..and A don’t want to disturb me with B and let me be with B..

When at the library..i wanted to sit near A but A shooed me away for me to sit with B..whats with her? Cant I be with her? Its like she cage herself and scared to be near me because she scared of B..

Im sorry for the long and confusing problems and a lot of grammar error but what can I do? I feel so bad about this