Overly dependent behaviour?

Cats are solitary creatures. You do not need another cat, and with his issues he would feel very threatened by another cat. They know when we save them. He loves you. The bathroom thing may be his curiosity. They also love running water. I have found that sometimes they like a non-threatening, very soft stuffed animal, or a blankie. They are like toddlers in their thinking. If you can find something like this to be a security blanket for him when you are gone, it will help. A piece of your clothing with your scent on it- like an old tshirt that he can have near him when you are gone will also help. Say goodbye when you leave, and greet him when you return, so he understands that you don't just "disappear" unexpectedly. Reure him that you will be back and give him his toy/blankie/youshirt. As long as he is not severely distraught he will relax in time. If it is more than just dependency and an actual anxiety problem he may need some homeopathic drops or something to calm him- Rescue remedy is what I have used. Or you could ask your vet. Remembering that he thinks like a toddler should help you with dealing with this.