I can definitely relate to feeling guilty over responding like that. My personal two cents is that you don't owe him anything, he is the one who owes you an apology should you ever cross paths in person. He was wrong to text you when he was drunk and say hurtful things, regardless of whether or not he may have mental illness. That doesn't excuse bad behavior. Remember, he is not your responsibility. He needs to own his words and actions. You set boundaries with him and that is okay. I hope this helps, and I promise that in no way is it meant to sound critical. I think you handled the situation a best you could in those circumstances.