Ask yourself which woman you are happier with when you're with her. There's no sure fire way to know if you leave your wife you'll regret it later so don't even try to find one.
However, if you're not happy, don't stay in a marriage for the kid. Your kid would want you to be happy and if it's with another woman, so be it. It's bull to say your kid would be happier if you were with your wife. What if your daughter has to watch you and your wife fight everyday and grow up in nothing but resentment and animosity?
I suggest a lot of soul searching and thinking on your part. I wouldn't say anything to your wife until you've made up your mind. Good luck.
