A good friend of mine made a comment today which is worth sharing...
Friendship is not about keeping score. Friendship is about giving love.
You are not friends because someone does something for you. You don't keep track of what you do for them or because they paid this time and you pay next time.
You do nice things for your friends because you like them and you want good things for them. And anything you can do to make their life better you do. And the good news is that if they are your friend they are doing the same for you. Win-win.
Lately I've been lucky enough to be surrounded with exactly those types of people (though I shouldn't say "lately" as I've been lucky enough to have those types of people in my life pretty much throughout!)
It's such a lovely and giving way to look at friendship.