How could i foreget my exboyfriend

Look

I doubt that he kisses his girlfriend just to make you jealous. He's probably just moved on, and you should too. Everything happens for a reason, so if you move on like he did then you'll find someone new also, and probably be even happier than before!

Sometimes good things fall apart so that better things can fall together.

Whether or not he is doing it to make you jealsous isn't really the issue. He is playing with you either way. Is that you in the picture? If it is, you are such a cutie I am sure you could get any guy you want, so don't settle for losers who want to mess with your head.
As far as forgetting him - out of sight out of mind. Don't go where he's going to be, and if you see him - leave. Also, get rid of any momentos you have from him. Even have a little goodbye ceremony as you throw it out. This really helps. Good luck!

It's going to take a lot but you need to get over him. I know it's hard but it will be the best thing for you, you are a pretty girl who deserves to be treated with respect and kindness. You can find someone much better.

Take some time and try hard to avoid him. Not interacting with him will help detach yourself from him. Once you are over him you will be freed of the sadness and be able to be independent and happy.