Drama

I have this friend ive been friends with for a long time and she is my best friend. Lets call her Ava. Well after she got a boyfriend she has been acting weird. They got togheter at the start of the school year and at the same time i got a crush on her boyfriends bestfriend. Lets call my crush Peter and her boyfriend Ben. They three got along well and they always considered us a group, but it didnt feel like it. It felt like Ava only cared about them and because of that i tried being more with our other friends. I also noticed how she would be really close with Peter wich i didnt think much about til prom night. 

So at prom night she is constantly on Peter and almost not even with me, but the line crosses when she asks him if she can sit on his lap(he rejects) and leans on him all the time. Mind you her boyfriend were right beside her. This isnt something i can rightfully be mad at as im not with Peter but i feel like she is constanlty ignoring my feelings, not caring about what i could feel and that she is really into Peter. 

After the weekend passes i get back to school and i talk to Ben. He tells me that Ava has been feeling left out when im with our other friends like i feel with them. I feel bad about that, but i have tried including her and i dont know what more i can do. 

What do you guys think i should do?(If even anyone is reading this)