Love isn't just about finding someone who will do something for you. There's much more of an exchange in love than that! I'll be yours, if you'll be mine; I'll sing you songs, if you'll play along.
There are times to be selfish, but being a really selfish partner is not one of them! You can't expect emotional support if you don't give it, and you can't expect trust or commitment if you're not giving it, either!
When there's only one side giving, and the other side doing nothing, they might as well disappear, because they aren't part of the love equation at all if it comes to that.
I'm not saying this will always be a perfect balance, or that all things must be given in equal or parallel ways. But some exchange must occur for this to be a true, long-lasting love.
After all, for hands to be held, both people have to move their fingers.