The best advice I ever got on this was ONE sentence from a mom whose son is EXACTLY (to the day) my eldest daughter's age...he had started dating but my daughter had not. The mom was telling me about how he talked about kissing his girlfriend, and I gasped (I really wasn't prepared for her cool-headedness!), and her response was: "Oh, no. You just cannot get upset; smile at all costs and LISTEN."
It's just the best advice ever. Even if you're not happy, all you can do is hand out advice, expectations, and information. We set limits, we help make the rules, we provide a safe place to talk...but above all we have to want to listen, and they have to know we want to hear what is REALLY going on.
It's the hardest thing I ever did, LISTEN to my girls talk about their boyfriends. But it is still so worth it, and the rewards are amazing.
It sounds like you're doing a great job.