I am sorry that this conversation came up, but at least you now know that he's not moved one inch in the mental department from years ago. You handled the conversation very well and pointed out a few things to him.
What I find interesting is that he wants to play the martyr if you find someone. He is more than willing to fall on his sword and do the right thing, i.e., move out if you meet someone. He is still hoping that you will make the decision about the marriage. He doesn't want to be the bad guy and leave on his own. It's all about perception and he's waiting on you to make the decision for him.
HaWho, you need to take some time this summer and reflect. There's no way to predict what the future will bring, but you need to think about the present and how his behavior may be affecting not only you, but your sons. There is no guarantee that he'll recover unless he seeks professional help in the way of AD's and therapy and even then, he may not recover.
Take it slowly, don't make any rash decisions at this time...you've got plenty of time to decide what it is you want for yourself and your sons. Maybe him moving out might be the best thing for all of you. Living in the dorm room may be keeping him safe and he needs to be like the little bird and attempt to fly from the nest. He'll never know what the outside world is like, at his age, if he doesn't get out there and explore it. I think he'll find that he had it good at home w/you and his family. However, that's my .02 for the day.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.
