AITA for coming down on my son after I read a rude text he sent to his girlfriend?

So this is an 18 year old son, and he is a senior. He is planning on going to college in the fall, but is going to a local junior college because he did not do wonderfully in high school. He has been with his girlfriend for almost 4 years, and they have planned to break up when they go to college. This is their plan.<br><br>So what happened is that the other day, I was preparing breakfast for my son, as I usually do. He is a picky eater, so the breakfast is usually just making a protein shake, with a bannana and milk. Sometimes he'll have omelette. On this occasion, I was preparing an omelette, and my phone was sitting on the counter. It was just sitting there, face up, and there was a text from his girlfriend on the screen. <br><br>The text conversation started with him asking her if she was coming over to help him with studying. She responded with, "I'm sick". Then he responded with "Ok, so you're just going to sit on the couch all day doing nothing?" Then she said "yeah, I can't do anything". Then he said "so you're too good to help me with my homework? I don't have much left and it's all easy". Then she said "no, I'm sick". Then he said "you're not that sick". I was amazed reading this, so I showed my son the texts and said "dude, you sound like a borderline abusive boyfriend, and she isn't even your girlfriend anymore". He said "I didn't mean it like that!!". I said "no, I'm going to talk to her parents about this, and you're grounded for a month". He said "I'm 18!!!! I'm an adult!!". I said "I literally buy every single thing you buy, and this is my house, so you will do what I say until you move out". He said "I'll leave". I said "don't let the door hit you on the way out". He said "fine, I'm leaving, and my life is going to be way better without you in it". I said "don't contact me". He left, and he is now staying at his friends, and he's been ignoring my calls/texts so he can be the victim.<br><br>AITA?