I've had to go through this before. The last boyfriend I broke up with was initially a friend, so we had the same group of friends and it became difficult. Luckily for me I am at uni, so there were times when I was away from it all, and this helped. It will be painful if he finds someone else but you will get through it.

Is there anyway that you can 'avoid' seeing him until you're feeling better about the whole thing? I'm great friends with my ex now, but this is only due to not seeing him much after the break-up, so avoiding the hurt.