I mean you went into it looking for a fwb type relationship which you got. You told him this and then you changed your mind but didnt tell him straight up so if he is just using you for sex that kinda was the arrangement initially. He isnt a Dbag if initially you both wanted the same thing and you havent informed him of your change of mindset.

Best advice is to have a talk with him and explain that you had a change of heart and would like to pursue a exclusive relationship. If he isnt up for it that's fine but you were honest and set what you want.