What do i do if my best guy friend and his girlfriend are both my bestfriends and he doesnt know she tells me whats going on between them?

well im bestfriends with them both but i kinda sleep with the guybestfriend and my friend doesnt knw.? but i know that he tells her wen are they going to “do it” and i always ask him questions like if he still loves her etc and he says he doesnt, but the next day she tells me he told her that he loves her what should i do.? im so confusd