((maymie)) - I don't think you should feel guilty for going on with your life. I think you should in a caring way, tell her how you feel or write her an email. You want to word it in a way where you don't sound jealous but you're concerned for her welfare. You should be able to go shopping or out to dinner, just mother/daughter alone time.

At the top of this forum, there a sticky post which gives some of the warning signs of an unhealthy relationship.
http://forums.psychcentral.com/showthread.php?t=134233
Try not to let this man get in the way of your relationship, where you stop seeing your mom. Could you tell her "mom I would really like to spend some quality mom/daughter time that doesn't include your BF". Explain that you don't like the way he treats her.