Moral difficulity?

A friend got a girl pregnant and she is due next month. However, information has come to light that the child may not be his and that at the time the child was conceived she slept with A N other. This information came accidentally from some of her friends on a drunkin nite. My mate has already spend a couple of thousand making a nursery and buying kids stuff in the anticipation of being a father. He is fighting to keep together with the mother (who is volatile at best). Do we tell him the additional information and ruin his dreams? If he demands a paternity test, it could jepordise his access to the child if it is his. She could also walk away from him with all the stuff he has bought for her and the child. What do I do?????