Yeah that was a dick move man but, I mean on her part too she could've at least broken with em before hand then maybe got with you a few months later. Look man what you did was wrong from a friendship stand point and, it sounds like you owe him at least some dating advice or a hookup or even hooker dude. Cause yeah he is lost and you definitely did break his trust and that takes time to forgive and rebuild back up. If you did this to me I would of ended things in a puff of anger and other things I wouldn't mention here as we don't need to go there. However just do something to make up for it since he's at least trying to work things out. You really did something awful to em. I don't know how you sleep at night but that really is dickish.
@Vd22 why the disagree?? OP clearly doesn't care about his friend if he stirred his friends jizz inside his ex.
It depends I mean if its like some ex from long ago, go ahead don't care. All my ex's are ancient now in terms of love life and time periods between hookups. In fact I don't even talk to any of em anymore. I still talk to my friendzoned "friends' though sometimes. So if y'all want someone's ex to put ya jizz in I'm your man. That is if you can find their numbers or snapchats.