The ultimate reasons why I broke up with her which I still doubt myself for were:
1. Her getting phone calls and texts from guys (not setting a boundary to keep them away)
2. Her being too touchy with guys (holding hands, for one)
3. The discrepancies between wanting to see me all the time vs needing space vs ceasing contact for days on end. My sense of security in the relationship was always being jarred.
4. Late in the relationship, her admittance of having sex with ten different guys while she was with her ex and my belief that, despite her saying she was ashamed of it and wanted to change, that she was still like that. It suddenly made the need for space, the guys calling, etc, seem like it was all related to cheating behavior. Even if she wasn't cheating physically, the needing space, the sleeping with her phone under her pillow, made me feel like something was awry.
... .
If I could feel/know that ending the relationship was 100% right, I'd be at peace. But the doubts keep my hanging in limbo.
So many great comments in this thread. In end, after all the layers are peeled away, it really is all about us; our reactions, boundaries or lack thereof etc. Given a choice between a magnifying glass and a mirror I'll reflexively grab for the magnifying glass. But the real answer comes from the mirror (the ten thousand pound mirror.)
Still I'd like to comment on your recurring question as to whether or not you made the right decision in ending the relationship. Struggli, if your best friend came to you telling you about his new GF and his concerns about her, and he listed everything I've quoted above, what would you tell HIM? I know what I would say.