A breakup is bad enough, but it sounds like this is also bringing up a lot of general pain about your life and feeling isolated and lonely. It must be awful, I'm sorry you're going through this.

I think you need to look at these two things as separate. You need to grieve the loss of the relationship for its own sake, and allow yourself to express what you miss about him as a person. Separate from that is grieving for the fact that you had someone, some closeness, and now you feel the pain of missing that.

The reason for separating them is that your healing from depression and loneliness doesn't have to depend on him being in your life. It's a different issue. So you can go on, and you can keep working on healing generally and getting to a point where life is better for you.

Do you have therapy? (counselling, not just someone checking in with you and giving you meds.) When you say you're completely alone, it sounds like it would help to have a therapist you can talk to and get support from.

It's not about "fixing" yourself. This isn't like a broken bone. It's about gently looking at difficult feelings and anxieties and learning how to cope with them and be kinder to yourself. Meds can help you while you heal, but they don't heal you on their own and they definitely don't fix you. Can you talk to your doctor about counselling?