That sounds incredibly rough--I'm so sorry you're going through that. I'm recovering from a breakup myself where I was the crazy ex, though my ex wasn't nearly as bad to me as yours. I was really traumatized, and I'm not fully better yet. But here are a couple things that have helped so far.

Forgive yourself. You made some mistakes, you did some crazy things, some wrong things, you took some shit, and it's okay to let yourself feel bad about that if you need to. You were in a lot of pain, and you're human. You're allowed to mess up. You can be a good person, and a good man, and still have messed up a lot. It's moments like these that can push you to become a much better person, because you need to if you want to escape the pain. Also, anyone, the handsomest, smartest, greatest, most mature person can end up in a one-sided relationship with someone who treats him like shit or cares less for him than he does for her. I'm not saying this is true of your relationship--but even in the worst case, most adults understand this.

You've got to fill your life with things, not just get over what's troubling you. It's all about your mindset, gradually shifting your focus to other things that fill your life and fully engaging with new experiences you have without her.

First of all, you need to address your depression. This part is not about her: it's about you and your mental health, and it's probably coloring your view of the whole situation dramatically and sapping you of the energy to turn your mind to other things that could engage you.

Professional assistance may help, maybe including meds. I honestly didn't find this very helpful myself, but I know some people who have found this invaluable to get through really traumatic breakups. Personally, I found that I had to start doing things again. I totally get that at times, you don't have the energy to set an exacting routine. But you're going to work, that's good, and beyond that, maybe try to set small tasks for yourself--very easy things to check off a list that can make you feel good. Even just, take a shower, do the dishes, clean this room of the house really thoroughly. And slowly work your way up, like rehabbing your mind.

People also recommended exercise to me, and I found it really annoying. "What, you think this is my fault? All I need is to pull myself up by my bootstraps and buy fucking running shoes?" I eat my words. That shit helps a lot. Just running a short distance, even just a mile or two if you're out of shape, 3 times a week. You can do it!! And seriously, give it a couple weeks. You will start to feel it.

Isolation is also really not great for you! Would it be at all possible to have a friend or family member come stay with you for a while? Or even take a short vacation and spend some time with a really close friend who can hang out with you a lot, force you to have some fun and go out, comfort you, and give you space as needed?

And sometimes it helps to change your surroundings, just change everything drastically. After being really depressed at school for a semester, I took a leave, started to explore new career options, and traveled around the country visiting friends and family. Think about the different things you could do, be creative, and see if anything feels really positive or hopeful to you. Maybe go for those things.

It's really hard for me to comment on your relationship based on what you've said. All I can say is, deep down, you know the truth of what happened, even if the depression and your process are confusing you now. You know whether there was something real. Either way, it's a challenge to accept. But you must accept your best guess for the truth and accept the loss. Easier said than done--and not something I've figured out.

Hope this helps, good luck. :) Thinking of you.