Why does "right guy/wrong time" come into my head now and then?

You were or are not smitten with "him", you are smitten with what you saw in him. You don't even know him so you cannot say you were smitten with him. Once you really know someone then perhaps you can say that. So take what it is you liked about him and look for those traits in someone else. He comes into your head because you liked what you did see. Just keep in mind that was a tiny part of who he is. And one should never be smitten with first impressions because those could easily be faked.