I've seen people in relationships where the couples are in love or at least claiming to be. Than the guy has an opportunity to trade up & well needless to say... he usually does. Sad but true, why? I dont really see this occur in women. They usually stay if they are content.
Obviously love is more important but she has to look good first of all for me to like her. Then, just as important, is her personality and other characteristics that I find attractive in girls. (Smart, funny, energized, open minded, loving, honesty, etc.)
The most "needless-to-say" thing is what women do when they can "trade up". Ever read research on both genders' sexual behaviour?
Females are hypergaming: they'll leave their partner for someone they see as "higher". Males are polygamic: they'll look for other women even if these aren't "better" than the one they have: jsut for the sake of variety.