Most Helpful Guy
You wait. They say time heals all wounds and in terms of getting over someone... it WILL happen with time. It may take a year or more but it will happen.
Most Helpful Girl
I'm guessing you are either in school or work with him. I'm in the same boat getting over someone who went from besotted with me to dating someone behind my back and acting like I was after him. He even told my colleagues that I liked him when it was him at first and I just responded. And now these people tease us. Here's what I'm doing because I still have to see him every day and I want to show him what he lost by being a horn dog...
1. Ignore him and truly don't care, don't try hard on this one or you will look desperate
2. Talk only about work when you have to
3. Stop all texts
4. Stop all iming at work
5. Show other people more attention than him
6. Be happy at work and really be good company to all others
7. When he brings his new fuck buddy over, be very nice to her and show how classy you can be
8. Always dress well and be well, work out and improve your life
9. Force yourself to date others until you did someone better than him, this will take time, especially if you care about the present jerk
10. MAYBE he will come around or if he doesn't, it's his loss as you are on the mission to get someone way better. Find someone that will make him feel inadequate