Why should it bother you and why do you even need to question him??? You don't want him so he's out there looking for someone else. He hasn't found her yet but nothing wrong with having a play. You seem to think that because he caught some feelings for you and you aren't ready to reciprocate that he should sit around with his finger up his arse waiting until you are! Got news for you...no one is that "Great" that a guy is going to hold off and wait indefinitely for them.
You don't want him but you don't want anyone else to have him...think you are the one with the problem!