What's the best advice for my son? He is so broken hearted right now. help me help him?

My son's girlfriend just delivered her baby. My son went to every dr appt. listened to the baby's heart beat, saw the baby on the ultra sound, felt her kick, was in the delivery room, he held her first, he put the first diaper on her, and he loved her long before she was born. He even bought her first dress ( among many other things). He found out while taking a smoke break during labor that his girlfriend had slept with at least 3 other people during this time. There were several other major issues that came up, things that he could not live with. He turned against her immediately. He still went back into the delivery room, rubbed her back, fed her ice, put cool towels on her brow even though he learned all these things. He decided on the spot that there was no future for them but he was going to be decent about the whole thing. He stayed for the baby. His plan was to claim the baby no matter what because he loves her so much. My son spent the night at the hospital after the baby was born. He was ok because he had no qualms about claiming the baby. He went home the next afternoon. Two hours later the girl had another man(possibly the father) to stay the next night at the hospital with her. This possible father wants the baby too. The baby looks nothing like my son therefore he is almost certain he is not the father. We think the baby may be bi racial because each day her color gets darker. We are not prejudice, it is just a definite sign that my son is not the father. We do wonder if maybe the baby is a touch juandiced. She has used him all up. The girlfriend admitted to all of it. My son is so broken. How can I help him? He says he feels as if he actually had a child that has died. He stayed up crying until 6 am. He can't look at baby commercials. He can't look at the many pictures of him with the baby at the hospital. Do I encourage him to get a dna test? It is doubtful. The girls mother said that the girlfriend was tanned looking when she was born, so maybe that could be the deal? Dna test or forget it and try to carry on? Plus, please most of all, help me help my son.