This is a really hard situation. Granted if I were in your shoes, I would probably feel the same way since I hold grudges easily. However, I think is a very sticky situation. Someone is going to be upset and I think it would easiest to determine if it's worth upsetting your mom and risking her not coming. I would just consider that risk and determine if you would be happier with your mom there with bf in tow or your mom not there at all.
Honestly, after going through the whole wedding day emotions, I think you would even forget that the bf is there. I felt like I was floating on a cloud and I was completely oblivious to everything outside of my hubby and I. I highly doubt it would impact your wedding much- unless he's an ass and would make a scene or something. You didn't hint at that though as a problem.