Can anyone recommend some good self-help books?

I am struggling with depression and have been obsessing over an old relationship for WAY too long. I desperately need to find some good tools to help me refocus my energy and attention into my own life and stop dwelling on failed relationships. Would love to seek professional help but I don’t have health insurance right now and can’t afford to pay out of pocket. Anyway, I was thinking a good self-help book would be beneficial. Preferably something I can find at the local library. Any suggestions? Thanks!