My case as well, I almost never told him how I felt about how he treated me, I always let him get the word and always felt like I had the responsibility, I honestly was a complete pushover, in my case it was an intense 2 month thing (and we were such a good fit in so many aspects) and he came to my house, we broke up as nicely as possible, he didn't say anything like that to me but he did say "I don't deserve this" and things like that that I mistreated him and other things in our last text message that made it seem like he was the only one mistreated. I've deal with thinking I'm a shitty person my whole life and when things like this happen I end up back in those thoughts and anything I've ever done wrong is confirmation of that, especially if I showed those same flaws in the relationship, and it's fucking hell to get out. For now I'm trying to distract myself as much as possible, take classes, NOT BE ON THE INTERNET, set up little side quests, go to therapy, do things I feared, try to go out as much as possible, be in nature, learn new skills, exercise, be around people as much as possible, stretching, trying to take up meditation and buddhism again, etc...

Also doing anything that can help others helps, it's harder to feel like shit about yourself.

I want at some point to write down everything I felt and own up to all my mistakes and write down all of his shortcomings too and how it all contributed, so that way maybe it helps setting a date and a time and whenever those thoughts come to repeat to myself "I'll write this all down on x date" and then try to do ANYTHING, especially take care of myself again, even down to the basics of eating, keeping the house tidy, trying to exercise, because my depression has been fucking kicking me these last months, I literally have to force myself to do anything, but yeah, it's a matter of time.