There is a common saying that goes something like this, "When you see a couple, normally, one will be extremely gorgeous while the other will be so the other extreme!" Well, no statistic had been proven but then again, it does look quite like the phenomenon. That sound so wrong but it just depends on the individual, what is pleasing to the eyes.
If one were to engage in a logical approach, it could be explained that the good looking partner must be getting too much attention that he/she knew exactly how risky it is to have a bf/gf that is that good looking. Thus, settling for a person with a stability out-look! lol
Personally, I really do think that things happen usually without any reason. You could find a person really ugly but after awhile, you will be like fly to rubbish (Since that you claim that the other party is really ugly, that must made you a fly!) It really get stuck into you. May it be you are just too used to that person hovering around you daily or just the fact that you started to appreciate that smile, gesture or even those brainless comments.
One thing for sure, it takes more than a million reasons why you hated someone, but it sure take just one unexplainable reason to love another. If love could be reasoned, it is functioned by the brain and never the heart. Whatever it is, I guess that that person must be really happy where I am now, even if he is facing a really hideous looking partner! LOL