Need advice

So before I started dating my s.o give years ago his sister and I were really close 
That's how I actually got to
Know him
So when we started seeing each other which we did try ask/tell her she totally lost her sht and stopped speaking to us both
Recently they have made peace but she still hasn't made a move to
Mend things with me but she and my s.o have and now I feel he is differnt towards me and I feel she has something too do with it I get tbey r blood but I'm really not coping :( what do
I do :/