Thank you all for your replies. If you are wondering, in these situations, I s usually look for someone to talk to, but a ton of people weren't available at half past midnight, so I drowned myself in YouTube and video games per usual.
I realized a little better what my feeling was later; I would actually feel sick when I thought about it. To expand though, I actually think they are really good people for each other. I know it will hurt a lot if I see them together, but it's likely that I won't anyway. Onto that last question from
>>4, do I feel betrayed? This is really hard to answer definitively, but I think some part of me does. I always felt like there were things toward the end that she didn't tell me, but I also don't know if she really knew what they were. The worst is just knowing that we mainly broke up over lack of time together (I was mostly free, but she was in school and had two jobs), just to see her now with someone else. I very much don't want to think that was an objective purpose; I want to see it as coincidence. Sorry for rambling on. In summary, I do feel a bit betrayed, but I don't have any specific reasons or persons behind any blame for it.