It is very common, as someone pointed out already, for adult children to resume the "child" role when they move back home.
I don't believe that it is uncommon for the parent to resume their "parental" role against the child's wishes.
Even though I'm the only one defending my point of view, I think it's very important to decide the difference between "House Rules" and "Control"
Examples of house rules:
- No wild parties
- No loud music after 10:00
- Contributing to the housework
- No modifications without consent from the owner
Examples of control:
- Curfew
- Restricting association with certain people
- Punishment
- Threats
The examples I've lister for "control" are fine for a child, but don't work well with an adult. One thing to keep in mind is if she wasn't living with you, she would still be doing as she pleases with this guy.
If this guy hasn't caused any problems for you personally, he is completely your daughter's business. There is nothing wrong with telling your daughter your opinion about him, or your opinion on how she's handling her life, but control is going to take a toll on your relationship with her instead of her relationship with this guy.