Here’s some research that confirms my own empirical experience–that people become more (or less) physically attractive to you the better you get to know them, depending on other aspects. I’ve noticed that women to whom I woudn’t necessarily have given a second glance upon first exposure become quite physically appealing over time and repeated exposure, if they have other desirable characteristics–they “grow on you,” as the old expression goes (for me, intelligence is a key enhancer).

This is probably a useful evolutionary trait, assuming that monogamy is a useful evolutionary trait.