This comes up time and again, but it boils down to this: religion is man-made and thus morality is too. Clearly morality doesn't require a judge/jury/executioner in the sky. There are devout Christians that cheat on their wives, murder their neighbors and steal from their friends, just as there are atheists who are genuinely moral people. Belief in an imaginary friend doesn't automatically make you a better person, and even if it makes you behave a little better, I'd still contend that you'd have to be a pretty shitty person if it takes threat of eternal torture to get you to be nice.
Once you give up belief in god(s) you may reevaluate aspects of your morality (views of homosexuality is a common one) but most will remain intact because it just makes good sense. There may be a period where you feel a bit lost, but once things settle down you realize you're the same person you always were, if not better off.