No. You are not.
I also have an 18 year old son at home (about to leave for boot camp). He and his friends tend to make spur of the moment plans, so he is reluctant to commit to a specific time he will be home, and I understand that. However, he is in communication with me via text at some point to let me know when he expects it will be, if it will be late. When he is working he is home before midnight during the week, so he can get up the next morning.
When he is not working the next day, he has come in as late as 1:30 a.m., or has texted around 1:00 a.m. to say he is just going to stay at his friend's rather than drive home (we live approx 25-35 miles from where most of his friends live... in the boonies, while they are in town).
It hasn't really been an issue on nights when I have to get up the next morning, but there was one Sunday night he went to a late movie and was just going to stay at a friends, but then decided to just come home after all. I was annoyed with him b/c he texted to tell me he was staying, i went to bed, then he texted to say he was coming home, and I can't go back to sleep when he hasn't made it in yet so late.
Generally he is super considerate when he comes in... quiet, doesn't wake anyone with the door, or cabinets or anything inside. But like I suspect is the case for many moms, I don't rest well until he is home. So a work night for me, is hard if he isn't in before 11:00 or midnight. I did tell him that, and he is pretty good about it. Not sure if it is b/c he is aware and cognizant and considerate, or it just works out that way b/c he is working or his friends have to get up to work, or whatever.
But is it a reasonable expectation that he let you know what his plans are? Yes, but not in the same way he did when he was a minor and high school student. (at least, that's my opinion.) He is living in your home, and must be considerate of the rest of the household. But doesn't really have to have your *permission* to do things/go places. I solved half the problem by just telling him that I wasn't planning on him for dinner unless he specifically told me he would be home. Too many times I expected him only to have him text or call and say he was going to Jacksonville with a friend to look at a car, or was going to a movie, or had a date or whatever. Nice that he shared, but too late to alter any dinner plans I had made. More often than not, he was not joining us, so I went with the averages and just said, "I'm not making anything for you unless you tell me you'll be home to eat." There is always deli meat and bread for sandwiches, or frozen dinners in the freezer, so ...
You do have to stop micromanaging him. You do. He isn't going to know what time he will be home when he sets out in the morning, most likely. I remember my early college days. I didn't know what the evening would hold by lunch most days. It was an evolving thing as the day wore on. And as a young adult, many times plans with friends were decided on AFTER work was over... after 5 pm. Depending on how you felt then. As long as he is being respectful and considerate when he does come in, and communicates (at some point before you feel the need to send out a search party) what time he expects to roll in, then I think you have to let it go a little.
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Also, I found that when I just mentally checked myself out of being his monitor, and stopped allowing myself to plan around whether or not he would be home, and stopped asking him about his specific plans... he started contacting ME to say "me and XX are going to the movie." I'd respond by asking if he was eating while he was out, and he'd usually say yes. "Ok, enjoy the movie. I love you."
His taking the initiative to contact me started when *I stopped* tracking him down for the information and demanding he provide it. (sounds harsh, but really it's just over-bearing-helipcopter-mothering)