When I was a collegian, members were allowed to miss a total of one meeting for personal reasons. Each time she missed a meeting thereafter, she'd have to write a letter stating why she missed a meeting. EC would then vote on whether to accept or reject the letter -- and then take any action necessary, usually a fine. Missing recruitment events/Ritual incurred the heaviest fine. Exceptions were usually made if missing the meeting was school-related.

Seriously though, if a member's dumb enough to say "I'm not coming to a meeting/event because I'd rather spend time with my BF..." then do you really want them as a member? Why bother even being in a sorority?