There is no way, if I was in the OP's shoes, I would leave that job now. Her BF obviously still wants to be around his ex, if he keeps hiring her back, when he knows she is not liked by the other employees and SHE KEEPS QUITTING. If the OP left the job now, she could not keep her eye on the ex and her BF.
Which is EXACTLY the reason the OP should leave that job and tell the BF to get lost.
There are other men out there--you'll find one who will respect you and treat you like a princess. You don't need to put up with this. You deserve better.
I wish things could be different, but I know that wishing for something just does not make it so. Lately I have been feeling that I do deserve better, I just feel selfish and arrogant for feeling that way, I suppose. Writing it all down makes things a lot clearer for me. Now I just have to find the strength to do what my mind knows it has to do, and what my heart dosen't want to...
It is so hard. Thinking about it is the first step. Do you live together? When things start feeling wrong they are. You need to move towards your real destiny. Think of this as a detour.... learn & grow from it. You can pass the wisdom on someday.