Anyone else thought this movie was unrealistic/ not believable

This is silly. It's not meant to be realistic. The entire movie is a bit silly, but it's about the romanticism of the characters, of fate, of their chemistry, and all of these things bringing them together. Just sit back and enjoy it and stop looking for realism :)

I took it as they were both getting married to the wrong person and they were looking for a way to get out of it. So they both thought back to that evening and wanted to see if they could find that person, and if they could that would be a sign not to get married.

I had the same issue as the OP. I just saw this for the first time but of course I had heard of it before, and I thought that it was going to have a similar setup as When Harry Met Sally or Boy and Girls where the main characters had a series of unplanned meetings that eventually brought them together in a romantic relationship. I was really surprised when that one chance meeting was the only incident that made them change the entire course of their lives several years later. I didn't hate the movie by any means, because it was pretty standard rom-com fare and the leads were both charming even if their characters were a bit wacko. But to me, I would have liked a little more development beyond that one night with the glove incident. Just my take!