guys don't have girl *friends*. they have girls they have slept with and girls they haven't slept with *yet*. i don't buy that but experience tells me that it's probably true in the majority of the cases.
i have a couple of guy friends that i hang out with that keep the fact that we hang out in my apartment discussing life, philosophy, and the freaking weather or whatever from their girlfriends. i feel kinda sad about that.
if the shoe were on the other foot, i wouldn't want that kinda thing being kept from me. if you're dating someone you have to trust them. a relationship with me isn't the same as being hooked up with the po-po you know.
i think by the time a guy has reached his latter 20s... experience has taught him to keep this kind of thing to himself rather than be open and be hassled by his girlfriend.
IMHO, that's a sad testimony to our society.
i would never be the other woman. it's bad karma. and i wouldn't appreciate someone being the "other woman" in my relationship. i try to operate by the old "do unto others as you would have done unto you" addage.
in fact, when my guy friends stray, i tell them to leave me out of it. i never want to be in the position where their partner asks me a question and i'm supposed to lie. i won't do that and i make it clear. it's true.