– I can’t put together, in my mind, these two things: “always been somewhat rocky”, and “we got along pretty well” unless.. perhaps you enjoyed his possessiveness, or you enjoyed the rocky nature of the relationship with him (?)

I wouldn’t say yes to either, we connected on other levels and those were flaws I was willing to overlook.

-but it didn’t die off a long time ago: M was trying so hard to separate you from W most recently because of his romantic interest in you still, don’t you think?

According to his words and actions, it did. I don’t think that’s an issue on the list here. To him the issue was that she was “replacing” him as my closest friend.

-why didn’t you want to lose a possessive man who was trying hard to separate you from your girlfriend?

Precisely because of our long history together. It’s not like he was absolutely awful, and I wanted to believe.

-there is some unclear (to me) connection between you and M, and the two of you together, through that connection, betrayed W- that’s my feel for what happened, at this point.

I’d say it boils down to the image of me he presented to her and the way he described the conflict. For some reason she chose to fully believe him and disregard all the struggles he caused to me and her, disregard the me she knew inside out. She began to assume a lot of things about my relationship with him, to blame me for things in between us she definitely has no idea about, to assume what I and he felt and what we didn’t, and so on.

She did mention feeling an unexplainable attraction and empathy towards him, and I didn’t think it could possibly lead to any of this.