This was literally me.
My boyfriend and I (also a male) were both 19, four years deep in a relationship, when he cheated on me. I ended up finding out indirectly, and broke up with him because I couldn't bring myself to believe that he wasn't lying.
I spent a whole month in communication with him trying to get him to admit to me that he cheated on me, but he kept denying, so I almost convinced myself to take him back.
Through the grace of god and great friends, I ended up not getting back with him, but I spent three months absolutely miserable. I couldn't deal with anything. I was a wreck. My grades and friendships suffered because I isolated myself because I couldn't do anything but think of him.
After the first three months, I picked myself up and started putting myself out there. I had spent 80% of my being out of the closet in a relationship, so I never got to see other people. I installed tinder, and I went out there. I met many, many people (including my new wonderful boyfriend, who I met in July and started officially dating this December, and am infinitely grateful for, AND who just may end up reading this if he so decides to stalk me (Hi Albert <3)), and I got to do what everyone deserves to do in their teen years.
No, that doesn't mean sleeping around.
I went on dates.
I made new friends.
I even ended up having my ex contact me around five months after the breakup, where we reunited and tried at it again, but I realized that all the time apart had truly made me realize that what he had to offer to me was all I craved because it's the only thing I'd ever known.
You can do this. Not only can you, and not only MUST you, but you know deep down inside it's the right thing.
If you two are truly meant to be together, your roads will cross in the distant future, and depending on how you feel then, you may want to go for it again.
But I promise, it gets better. You will be okay. Cut all contacts and don't be afraid to fall back on your friends. Pick up a hobby. Improve your mind and body.
She'll come back up every now and then, but you have to power through this.
You'll see, it'll be worth it.