SOMEONEHELP :'( i feel really upset!?

You're the only one who can truly answer that question, but if it helps, I'd end it. He's already liking this other girl while he was with you. The fact that he told you means he is ready to move on. Although it will hurt, you need to do the same. There will be others and there might even be more heartbreak. But that's part of life. Enjoy it and have fun!