Why don't you try talking to him about it, say that you don't feel comfortable with this person being so prominant in his life.
Magick is not the solution to everything and somethings can be best worked out with conversations.
if you really want a banashing spell I suggest writing one and learning how to cast one yourself rather than asking someone else to do it for you.
1) Rarely will people do this for free
2) If they do do it for free it may be a fraud or it simply won't work
3) For a spell to be truly effective, the caster has to be connected to the situation, that is why we always say that it is best to cast for yourself.
I really hope you find a solution to your problem.
Best of luck.