I think the reason you are thinking about him is because you were previously disappointed in who you he turned out to be, which left you inconclusive. You might have even felt rejected on some level by him by the way he describes his preference for skeleton ladies. Now that he's back and showing interest, the stimuli you have received from him has reactivated the unresolved feeling and thoughts you had before you met Seth. This will likely continue until the matter has been satisfied by questions in your mind being answered by working out the truth of the matter inside you. You are thinking with your head though and you know that guy is a waste of time and will probably end up hurting you and leaving you worse off than before. Stay in control of your physical actions like you already are. Firmly reject him. That could be a lesson for him in turn.