>>4 Sorry, thought you meat your friend.
Talk to your mom. Tell her you know that he could cheat on you, but it's also possible that you could cheat on your boyfriend, but you're better than that, and he's proven to be better than that as well. Remind her that relationships are built on trust, and without trust, ANY relationship will fail. Tell her he trusts you, so it's only right for you to trust him.