Don't beat yourself up, but I will tell you your son sounds VERY NORMAL! And your re-action is normal too! But I do think you can strengthen your relationship with your son if you learn to let go of your anger and some of your expectations.
Some kids are very responsible in the way you want your son to be. Others just aren't there yet. If it were me I would let it go a bit more. Let his room and bathroom be messy. As long as it isn't a health hazard.
Do you pay him when he babysits? I may get flack on this site, but I do think older sibs should get paid to babysit, unless Mom is just running a quick errand and the older sib is awake and at home. If your son doesn't do a good job, then I would pay someone else. I would think your 10 year old is capable of feeding himself.
His attitude is normal. If he doesn't get a job or help you then to me the consequences would be I wouldn't give him any money. I wouldn't want to come home to a disgusting house, but I'd let go of a perfectly clean house. He is 18, and he is MALE.
If he does attend college in the fall and manages to pass all his courses then I would say he is doing his job and let go of a lot. Our 19 year old didn't want to get a job this summer so we required that he take summer school to get some credits. He had a choice. Give your son a choice and make yourself be okay with what HE chooses. He is of legal age now and you can't make him do much of anything. If he doesn't work then HE pays the consequences, which is no spending money. He may be okay with that.
If you want your son to come back be careful. You can't let him walk all over you either. If you make an offer for him to return have a game plan and compromise. If that is too hard for you then being at your brothers isn't such a bad thing. He is in a safe place where someone loves him.
DON'T FEEL GUILTY. Teens are no picnic and we all struggle. Think about what your goal is for your son. Ours is getting our son through college with hopes that he will be self-sufficient.