Feel like ive been sexually assaulted

So i was casually hanging out with my friend and her bf we start drinking and her bf and i end up alone at one point and we are all tipsy as well so we got into this conversation and we are all pretty comfortable with each other anyways he goes and touches the top of my breast and immediately im like what the fuck do not touch me i have a boyfriend and ended up leaving i feel so sad i cried and i just dont understand what makes men think its okay to touch woman and act like its a joke afterwards im so sad and i cant speak to anyone about this i need some advice to get through it i could never tell my bf and ofcourse i could never tell her because of drama but i feel as if i cheated on my bf who i love so much and feel violated as well i feel like i need an apology and cant hang out with them like that ever again because i dont trust him and am sorry for her as well please help