Lon,(sorry so long)
If I was your mom (and I'm 48, so theoretically, I could be)... I would say that you should cut all ties with her. She is too young and wants to be a kind of wild and play the field. She wants to explore/experience life... but it sounds like you are ready to settle down. The whole on-again off-again relationship indicates to me that she is just using you when she has nothing better going on at the moment. Plus, the whole "friends with benefits" is a totally foreign idea to me. If that makes me old fashioned then that is ok with me.
I think I saw it best described in Reader"s Digest: "If you are searching for the love of your life...STOP!!! Start doing things that you love to do - that is when you will find someone with common interests that you can fall in love with."
So get involved in something you love to do... (tractor shows, hiking, photography, whatever interests you) or maybe some new adventure. Enjoy your singleness and be confident. And though guys are visually oriented...uhm, remember that beauty is only skin deep. You also want to spend your life with someone who has common goals, interests, a good work ethic, and a lot of brain cells between her ears. (My cousin, a really shy guy took public speaking lessons and dancing lessons to help him overcome it. He later met his wife dancing... they have been married over 25 years, have 3 kids and seem to have a great relationship).