What do i do, HELP ME!?

ok so lately i noticed my bf has been acting weird when we first started going out he totally showed he loved me holdin hands n holdin me even with his friends around, he didnt care. now he doesnt do that and hes immature and runs around like a little kid and just leaves me standing there all alone. and i HAVE to go to these parties where his ex is at and i hate her and she stares at me and i hate it. and then im left alone and i dont no if he still has feelings for her cause shes always around >=[ AHH