Sad to say but I think you may have lost this one.
Depends how the break up, was it slow, painful, basically a long time coming? - in this case he may have made his mind up.
On the other hand if it was a quick breakup, maybe an overreaction - you may be able to get him back, good sex could play a key part. Remind him what he liked about you in the first place, did you used to make him laugh, were you romantic. Bekind rewind!
The question is do you want him back, someone you think will dump you and go back to their ex? Surely you won't feel very secure in this relationship...
How long were you two together? Did him and his ex break up on good terms? Was she still part of his life while you two were together?