I am having trouble understanding the 2nd story.
Pretty straightforward, I think. Short-hair is in love with long-hair, although the latter doesn't know it. Long-hair fools around with guys, but never gets in anything long term. So she doesn't really love them. Circumstances lead to them having sex, which distresses short-hair because she's serious. Long-hair's actions at the end make it clear that she takes short-hair as a serious romantic possibility, same as she would with a guy. Maybe even more so.
Upshot is, long-hair is bisexual and there's hope for an actual long term relationship.