I'm so sorry you're having such a rough time. But you're grieving! Yes, grieving the loss of the relationship. And grieving can take a very long time.
There are 5 stages of grief: Shock, anger, depression, bargaining and acceptance. It sounds like you're between anger & depression right now. How long ago was it that you broke up with your girlfriend?
If it's been more than a couple of months, I'd suggest that you talk with your doctor and have him refer you to a good therapist. A therapist can help you deal with this. Or you can perhaps talk to a grief counselor -- you can get in touch with on thru Hospice. They have excellent grief counselors. I've talked to one myself after my husband died. You don't have to have used their services previously -- just give them a call and ask to speak to a grief counselor. It's well worth it.
I wish you all the best! I hope things ease up for you and you begin to feel better. Please keep us posted, will you? And God bless! Hugs, Lee