Hi C.,
First let me say that I agree with the other mother's advice. I am the mother of 5. My oldest is about to turn 20, then one turning 18 two days later, another 18 next July and one turning 16 in Oct. The youngest is 8.
So I just went through this with my oldest daughter almost 2 years ago and I had exactly the same anxiety. I think it is normal. I went throught all the same feelings of wondering if I missed teaching her anything she'd need to know to be sucessful in life. And there were rules to follow even after 18 while living at home. My daughter decided that wasn't going to happen and I did have to ask her to leave. She left and has been on her own since shortly after her 18th birthday. She works full-time and attends school at night, full time also. She has also never asked for a dime. She has thanked me for all the things I made her do (chores, etc). She has roommates as well. And she does complain about them being slobs and coming in late and being inconsiderate. So it comes full circle and she "gets it" now. So the answer is, yes he will be fine and you will have to trust in him and in the job you did. Sometimes they will have to make their own mistakes and learn. We did that too...remember? Good luck and if you want to talk further, I am here!
Hugs,
S.