Se heavy stuff ahead but since this is anonymous I thought it's best to include every detail within reason. And sorry for the length, again, I wanted to include every detail.
Unsure how to explain everything so I'll just go through it all in chronological order. Me and my gf met at university as flatmates. We got along quite well and quickly became quite close, doing a lot together even without her other friends we also loved with who she had known longer. Safe to say I developed quite the crush on her and eventually worked up the courage to tell her how I felt. I over thought it a lot and figured out a way to tell her without trying to be too forward, more of a "hey, I like you a lot. If you don't feel the same then it's okay, im not trying to ask you out, just getting this off my chest". She replied soon after and, to put it simply, told me she definitively didn't feel the same. Bummer, but I tried to move on. About a month later I was part of an event and invited her as well as a few other people. At said event everyone got reasonably drunk, which lead to her meeting and starting to talk to someone. I tried to ignore it and push it aside because we weren't dating, it was nothing to do with me, but I still had feelings for her so it became hard to ignore. After a week or two it got to the point of him coming over and them doing things together like cooking and watching a movie or something, nothing more than that as far as I'm aware. Again, it sucked because I still liked her but it had nothing to do with me so I tried to push it aside but couldn't. It ended up really having an affect on me, not helped by the fact I'd lost my mother about a month or so before so I was already in a bad place and me telling her my feelings to begin with was to just get it out there so it took up less headspace.
About a month later they had stopped talking and one thing lead to another and we ended up dating. A bit after we were having a conversation and I brought it up, not out of the blue or anything, we were basically doing an 'all cards on the table' and just saying everything we thought the other should know. I basically just said about how I felt during that time. She replied and told me that the truth was that she knew she liked me back from when I first told her, but thought it would be best for me if she left me to myself because of everything else I had going on and she didn't want to add any more on top of that. She said she only started talking to other people to distract herself from how she felt towards me and try to look for someone "just as good" but when she realised she couldn't find anyone else she decided to tell me she liked me.
The reason it's taken such a toll on me is because I had such a tough time during it all and at least some of it could've been avoided. Her reasoning adds up and she wouldn't lie about any of it. I don't doubt her love for me now or anything like that. It's just the fact that I can't wrap my head around her thought process. It's been the cause of many sleepless nights and I don't know what to do about it. I hesitate to bring it up again because I know she'll only blame herself and nothing new is going to come of it, there's nothing I can say that I didn't before and I don't feel any different about it but it's still taking up such a big part of my brain.
I think I'm mainly just asking for other opinions or points of view on it? I'll try to answer any questions but I have notifications off on Reddit so I'll check quite infrequently.