Threesome ruined my relationship :/

So I've been seeing this guy, and I was hanging out with him and his friend at his friends house. We were just sitting around, drinking and talking. We decided we wanted to watch some tv and lay down so we all headed to his friends room and hopped on his bed. Next thing we know we started having a threesome, but the problem is me nor the guy I was seeing enjoyed it and just didn't speak up to stop it. It really damaged our relationship and want to work it out.. how do you move past soometjing like this?? I need advice :/