Talk Guests and Behavior Expectations
Yes, at her own place, it was OK if your daughter came home tipsy and with a gentleman friend, but how do you feel about it?
Behavior expectations are tricky, because, as your son or daughter will quickly point out, they're paying rent. That should entitle them to some sort of privacy -- or, at least, an adult discussion with you.
The key is working out some sort of compromise. If you're not comfortable with your son bringing home overnight guests, then it's only fair to hold your tongue if he chooses to spend the night elsewhere -- as long as he texts you to let you know if you should set the house alarm or not.
What is your comfort level with drinking in the house? Smoking? Late hours? Try to approach this more like a roommate than with a "This is my house" attitude. It is your house, of course, and you get the final word, but having these difficult conversations with your child is how your relationship matures.