*shrug*
In the cold light of reason, sure, they look like bad decisions. I can't guarantee I wouldn't make the same stupid choices in the right situation. Emotions are messy. I stayed in a relationship for over a year once - a relationship I *knew* was a bad idea going into it - out of a combination of guilt, shame, lust, and despair. (The despair being, "Well, I'll never have another girl who's interested in me, so I might as well.")
Also, and I can't emphasize this enough, I think it's a mistake to think of them as a "couple" throughout most of the story. They really AREN'T each others significant other, not at that point; they're attracted, they're wooing each other, they're having sex, but they aren't really engaging, and that's been their problem. Haven't you ever seen or been in one of those relationships that consist of a date and a few days of, ahem, interaction and then a fight and months or years of abstinence (from each other, at least)?