Lonely and needing advice

I’m 18 and a freshman in college. My boyfriend and I broke up on good terms before I went off to college. We never had sex but came very close to it many times. I loved him and he made me so happy, so I always thought that we might reconnect at some point. Fast forward two weeks after our break up and he has had sex with some random girl, and at a NYE party he interrupted a conversation we were having by making out with a girl he didn’t know (he had been drinking). I know I should just forget him but it’s so hard. I know that I’m probably just lonely and he is someone I’m comfortable with but I just feel so depressed at the moment. I don’t feel attractive, and it seems like no matter how kind, funny, flirty I am.... I can’t get back into my groove with men. Ladies... how do you let go of jerks like my ex and be confident in yourself? Because honestly... I’m starting to question my self worth and I don’t like that at all.