21 year old needs help

Hey so I'm pretty desperate and this is the first place I'm going to for help. Ever since my ex girlfriend I broke up, I have not been able to have sex with anyone else. This worries me because I had the same problem before we got together and eventually she helped me through it. She is the only girl I've ever been with and now that we are done I'm scared she'll be the only. It has to be purely mental, I'm 21 and workout five times a week and play sports, so this must be fixed asap. I know I'm bigger than average down there but when I was a kid, I thought something was wrong with me because I wasn't circumcised. Now I have this fear that a girl will not want to have sex if I pull it out. Idk what to do, idk how to get over it, it's a reoccurring thought that I can't chase away. I'm already 8 days without masturbation, gonna go for a months at least..