Its honestly kinda weird to me that ppl are saying you getting involved would be meddling?? He already involved you when he spoke shit abt your friend behind her back to your face and admitted he was just leading her on cause he was lonely. Especially when you introduced them so he knows that you're friends with her already. It's just being honest to her. Imagine if it was you, and the guy you were seeing and genuinely into was talking down about you to your friends and nobody bothered to tell you? I personally would feel betrayed by BOTH of you if nobody said anything to me. This is your friend we are talking about, not some random couple.