It might help to notice when you are thinking about him. If you are on a date with another, does it come up if the conversation begins to lag, etc? Nature abhors a vacuum, and so, you might, unwittingly, be seeking to fill that vacuum with someone who fits the bill “better”. What are the qualities that you keep coming back to, that you want? Think of him as a set of qualities, not him specifically.
It’s really tough when you begin to obsess about a person. You really might need help to practice the skills to get over this, or it could interfere with future shidduchim. Please, don’t sit on your laurels and wait for time to heal this. I know from personal experience and from that of a very close friend who spent years doing exactly what you described that some people have a harder time than others letting go. It might be difficulty with loss in general that makes some hold on longer than others. I know someone who obsessed with a past shidduch long after the other person got married. You may think that that’s not you, but you have no way of knowing. Neither did she. If it’s interfering with your life it’s time to get help. You have to work on getting over it (or you might find yourself reverting to old habits (obsessing/comparing) if conflicts/problems arise in your future marriage (which they will; they always do).