My Son Is Grieving Terribly Over A Miscarriage! He Can't

My son is grieving terribly over a miscarriage! He can't move on. And to make it worse, she left him! She says she is the only one who should be sad because it happened to her! He is in really bad shape, grieving the loss of the baby and the girlfriend. I don't know how to help him! He is 23 and I have never seen him like this? Thank you!