Most Helpful Guy
Same thing happened to me and it bothered me for 2 years. Try to find something to do to take your mind off it. I started to weight lift to make my ex regret cheating on me because I'm more attractive than her current boyfriend. But honestly, only time will heal this as it won't be easy. This happens to everybody who gets out of their first relationship.
Most Helpful Girl
Nothing you really can do in these situations but surround yourself with your best girlfriends and try and get your mind off of this.
You my dear, have suffered a double whammy asshole - he knew he was your first and he was not faithful...
Getting over a first heartbreak is hard enough as is but for the reason behind it to be unfaithfulness - that is over the top and you really just need to take your time and move on. Heartbreaks heal only in time and while time seems to be doing a very slow job at mending your heart break and you may just feel like "firing" time at point - just to take care of it on your own... Truth is, time is the only thing that can heal your heart.
Call the ladies, have a pizza and movie night, go out for drinks with girlfriends and learn to smile again.
You deserve that.