I truly can't see how having a friendly day with someone before a break up makes them a pyschopath. Or not giving notice. What?? That's nonsensical, and the OP's feelings about the girlfriend seem to support how off the mark that assessment is. Breakups suck. If you give a warning, you are being cruel for not ending it as soon as you know. Likewise, if you try to make it part of a nice hike (for example), perhaps in order to show that you still care about the person but don't want to be in a relationship. If you give no warning, you are a pychopath. If you don't make it part of a nice day and just do it the moment you see the person, you are callous and cruel.
Some people just don't like it when a woman has the audacity not to be with someone, and not terms or handling of the break up is going to be acceptable. There's no good way to break up, because breakups are by nature painful. I know you still care about this woman, and it probably has to be hurtful to hear her spoke about in that way. I'm sorry.
When relationships end non-mutually, one party is usually left with all sorts of questions. The reality is that often there aren't answers to the things we want to know. "I just wasn't feeling it anymore," lacks anything concrete. It can't be fixed or really even understood. Much of the time, there is no "why" anymore than you could explain why you aren't attracted to that very nice, fairly attractive woman your friend introduced you to at a party. Sometimes, you just don't feel "it", or you stop feeling it, not because anything happened. I think the times where there is a specific relationship-ender (like differences in finances, or religion, or desire to have kids, or other major incompatibilities) are actually less common than times where one party just realizes that while the other person is great, they aren't a Forever person for that individual. It sounds like that is what happened here. So even if you did go to her and ask whatever questions you have, it's quite likely she won't have any real answers for you other than trite platitudes about just not feeling it, and it's not you it's her, and that sort of thing. You can't answer an unanswerable question, and matters of the heart generally defy explanation.
I would severe ties entirely. It may be more uncomfortable (or even painful) now, but that's truly the best way to heal. I don't believe you can be friends with someone you still want to be with. Let your heart heal, and once you feel it has, probe your feelings. If you *truly* feel you no longer want to be with her, then you can let yourself ask her to meet for coffee, is you are still drawn to do that. But only if you are honestly done yearning for her, and only if you are doing so to catch up with someone from your past, not to get answers about why she doesn't want to be with you.
I'm sorry you are hurting.