Different faith, but I have an old friend who has since become a rabbi. She's been involved with various jewish communities all her life, her career depends on her faith, and she's married to a conservative jew. She admitted to me that ever since studying various other faiths in college, she realized that there is no one true belief system. There's probably not even a god. But, she went on to do all of these other things that require "faith."

So here's the advice I'd offer on her behalf, just watching her as she struggles with this:

1. Don't walk away. Take it very, very slow. Nothing about your actions even have to change.

2. Understand that even if your beliefs have changed, your motivations have not. My rabbi friend still wanted to be a rabbi, still wanted to be a good wife, because these things brought her joy. She enjoyed knowing families and helping others, both in good times and bad, even if she wasn't doing those things on god's behalf. She was doing them for herself. And I'd say that makes her an even more selfless person.

3. If you have to phrase the discussion with someone who is fervently religious, ask them about any doubts they have. Really listen to them - don't immediately reveal your own conclusions. Don't reveal them until you have some idea that it's safe to do so. You'll find that most religious people have serious doubts, and are willing to discuss them. In fact, many people enjoy airing their suspicions; struggling with faith is a common way of reaffirming that faith. Some might call that cognitive dissonance, but many take pride in the struggle to better understand their religion.