ADD or not, the young man was very clear in his intentions. When you told him you wanted more, he said that he couldn’t give it. It sounds like you’re on two different pages. The problem is that you continue pursuing him, your feelings will only grow deeper and you’ll wind up hurt because you are more invested in this than him.
His behaviors are aligned with a person who is not looking for a full relationship.
I would listen to what he said to you when he told you he wasn’t looking for the same thing. If you do want a relationship, I would move on from this guy. Let him know you made a mistake, you do want more, cut the friendship you have with him and look for someone who is looking for the same things as you are.