The attraction system uses more than likes or dislikes to determine the attractiveness of other sims. Setting likes and dislikes only allows you to tailor or better tune things more to your liking. From what I can tell, not setting them means that the game sees them all as equal and other things then take precedent in the attractiveness system. I'm not sure what they all are though. I think the traits you assign might be part of it but pretty sure that's not all. Conversely, if you set too many things as either liked or disliked, that does pretty much the same thing. I've found it seems to work better to only set a few for each sim. Don't try to use the whole 50. So, for things where a spouse becomes unattracted to their mate, go in and try to make likes and dislikes for the two sims match so they like the same things. Also set the 2nd category for things like hair color and fashion too. You just have to experiment a bit to get the attractiveness to change to what you want it to be. Again, keep in mind, that if you set a lot of them one way or the other, you can end up with a lot of sims which become very attractive to your sim and vice versa. Setting too few will make your search for that perfect mate harder as well and you will have fewer sims that are attractive to your sim.
Hope this helps.
