I know how it feels on both ends and neither is fun. I will say that maybe he truly didn't realize that he might be able to positively contribute to helping you with your mental issues and is now going overboard because he feels bad for not trying sooner.
Another thing might be he just likes you and wants to be a part of your life. I've had periods where I feel alone or sad when my boyfriend isn't around because he's meeting with people I don't know or experiencing things I don't get to see. It's not really a jealousy or self-esteem issue but more just a desire to be connected to a person that's not there. It can feel terrible on both sides and it's best to talk about it if he is willing to.