your worship does not hinge on return favors
S'alright, Tink. God supposedly returns love to you, right? Don't you get to bask in his "presence" for being faithful. That's just as much (or more) a return favor as anything else.
I realized that all the good feelings from worship were coming from within. Living a clean, healthy life has its own rewards, regardless of who gets the credit. It feels good to think god is watching over you and cares about your future, but as soon as you go down that slippery slope of overindulgence in pleasures and unhealthy living, you'll find you don't feel so good anymore, whether you are Christian, Muslim, Jew, or Atheist or anything else.
Explain how an Atheist can have overwhelming feelings of spiritual insight and deep love for all living things, while across the street the believer fights the urge to kill himself (melodramatic, I know, but you get the point). It's the way you live that dictates your wisdom and happiness, not the whim of some giant in the sky.