Kick that boy to the curb. I was with my ex on and off for 5 1/2 years cause he was cheating on me And I always thought it was my fault. He was always trying to get with my friends who thankfully would tell me when he was. It has been a year and a half since I've even talked to him since I dumped him. He told a very Good mutual friend that he wouldn't cheat on me this time if I kept putting out the way I was. Cheaters can all go to hell lol. They know exactly what they are doing. Some love the adrenaline rush from getting caught. Let go of the dead weight and drop them both for good. Nasty scum bags. They deserve each other and they definitely don't deserve you.
Healing advice: Spit in an empty cup for one minute. Measure how much spit. Now redo to try to spit more. Empty cup by drinking spit. Took you mind off of it eh? Healing advice!
It happens a lot.. but the good thing is you're young ! You dated as teens ,and people tend to change as they age ,sometimes not for the better. Go out have fun ,and look at it this way they are both crappy and belong together. Just be glad you found out now rather then 20 years and 3 kids later.