He is a full blown adult. You are NOT responsible for him. I know you are his mother, but where he lives and what he eats is his own darn responsibility. Next time you see a text from him about food or needing money or a bill, send him a text saying that "you are sure he will figure out how to fix the problem". After all, he has figured out how to fix all his problems in the past, hasn't he?
If you are concerned about suicide, figure out where he is and send the ambulance to him, but do NOT invite him to your home. He is not safe to have around you. He just isn't.
As for him being off drugs, actions speak louder than words. HIs actions say drug addict loud and clear. They just do.
Focus your energies on your younger son and your wife and your poor abused dog. I am sure the other dog is nice when not agitated (aren't we all?) but she isn't a problem you can handle now. Your son knew what he was doing when he forced the dog on his sibling. He KNEW.
As far as knowing you love him, he does. My brother is a recovering alcoholic. He told me that even when my parents left him in jail for a couple of weeks, he knew our parents loved him. He wasn't sure I loved him when I wouldn't bail him out during that time, but he and I have a difficult history. His feelings are not my problem.
I strongly suggest you see a therapist with experience in addiction/codependence and you also attend NarcAnon or AlAnon meetings, the meetings for family members who have a loved one with an addiction problem. It really makes a difference.