My best friend's boyfriend made a move on me. Should I bust his shady ass?

Recently, my best friend's boyfriend made a move on me. He confessed that he's had a crush on me for a while, then tried to kiss me while his woman was in a different room. They've been dating for a while, and even live together, and for the past few months she's been talking about a future with him. I was drunk at the time, and he was sober, so I feel like he's being extra douchey for taking advantage of the situation. The reason I haven't snitched so far is because she is madly in love with him, and I can totally see her blaming me because she doesn't want to admit he's not perfect. So what do I do... hurt my friend with the truth and potentially lose her friendship and ruin her future plans, or fess up about what a skeeze he is before he starts trying to work the threesome angle?
Updates
+1 y
Ok, so apparently people are misunderstandin my post... we did NOT kiss, he just TRIED to kiss me and I STOPPED him. But I am concerned that he may try to do this again at some point, which is why I'm asking this question in the first place.
My best friend's boyfriend made a move on me. Should I bust his shady ass?
Post Opinion