So me and this girl have been friends for awhile and I know her boyfriend, the other day she told me that some girls were gonna tell him that she was cheating on him with me even though we were just friends at the time, this kinda set the ground world for the current situation 

She added me on snapchat and we started talking, one thing led to another and she ended up sending me nudes and talking dirty with me, and she really wants to fuck, and all while she keeps insisting she still loves her boyfriend,

It's just been weighing down on me mentally, I don't even know the guy that well, she just doesn't seem to care, the fucked up part is he still has no idea and he's still pouring his heart out to her.

What do I do here? I know its already fucked up I'm going along with it but like is there any ways I can fix it somehow?

I've been cheated on before so I know how much it sucks but this already went too far : /