Son was asked to be a pallbearer

I need advice. My son is started therapy next week because one of his friends took their life at school and my son and another one of their friends found him in the boys locker room. They were all on the same soccer team and their mom asked if my son could be a pallbearer which my son said he wants to do. I'm just worried that will be more traumatizing for him. It's a closed casket but at the same time he's already traumatized. Carrying his friends corpse may add salt in the wound. Not to mention the funeral takes place on my son's 15th birthday so this will be happening on his birthday. My ex thinks he's old enough to decide if that's something he wants to do. I worry about his mental health