arguments in the back o' the van

"If you can't be with the one you love, honey -- love the one you're with," means:

a) don't treat someone like shit just because you have/had eyes for someone else
b) be responsible to your partner no matter what
c) settle
d) if you're not in a relationship, love yourself
e) gee, Ari, I've always thought it actually meant [FILL IN THE BLANK]