Your mothers advice is sound. If you're serious about her, just leave it in the past. Hey, you went out and banged a girl and feel bad about it, that should be a cure to know you don't want to do it again and want to stay with this chick. You'll have to find ways to spice things up with her if things are a little boring, that can be dangerous.
“Where the danger is, so grows the saving element.” ~ German poet Hoelderlin