Well when I broke up with my boyfriend I started dating another guy and I still felt a lot for the ex. I texted and e-mailed him all the time and couldn't let myself get close to the other one. We had a lot of problems.
So, if he still likes her then he might have a hard time getting over her.
I eventually got over it and in total love with the new one. :)
So good luck, just don't let him treat you like dirt.