UPDATE:
OK, so get this. 3 weeks after this whole thing went down, we meet to talk (his suggestion) and I took that as opportunity to give him his things back.
He apologizes and tells me I've taught him a valuable lesson in life. But that he was angry with me for reacting the way I did, at a public place and even involving her. He says he wants to remain friends with me.
He then tells me that now he is EXCLUSIVE (ie MONOGAMOUS) with the other girl he was seeing because since I split up with him, our triad "organically" became a couple. And that it just "naturally" happened that way.
Let me clarify. The other girl, let's call her Cindy, knew about me. I knew about her. I found out about the highschool friend visiting here by chance, only because he drove by my place.
When I asked him if Cindy knew that his highschool friend was here, he said "No". I asked him if that was fair that she doesn't know, he said, "She would prefer not to know...but if she knew, she'd be mad."
He said that his relationship with Cindy became better now that I am OUT OF THE PICTURE. I"m thinking well, duh! Of course, Cindy always wanted to be in a monogamous relationship with him and now she's got it.
Do I want this idiot back? NO!
Am I pissed off? I am. But I realize that better Cindy than me having to deal with his lies and drama.
What are your thoughts?