I can completely relate. I have a very similar experience I am dealing with right now. I left someone to be with someone else and now I'm overcome with guilt and regret as I think I made a mistake. I've recently been obsessing over this girl and missing her so much. I've taken the step to admit to myself that I need to learn from it and move on but it is very difficult because I have trouble letting go of things. The biggest help for me was to start a journal, it really helped me to get my feelings out and not hold them inside.

It is not something that will take a few days to get over, it takes time. Sometimes I wish I could take the advice others have often given me but it is true, when we make mistakes, and it happens, the best thing we can do is learn from it.