He needs her — and wants her — so much that she feels guilty.
The first guy is about to move to the other side of the country.
Boy A and Boy B were friends, good friends, housemates even. It was apparent that Girl Z liked Boy B instead if A, so both boys sat down and talked about it.
Boy A relented, backed off, and gave the opportunity to Boy B, despite him liking her first.
Abby Cross is that slut girlfriend with the girl next door look.