Boyfriend planning his funeral.......

My boyfriend is 19 and he's been battling lung cancer and going through chemo. It's been so hard and I've cried and even started praying again. For no reason.... Because it's confirmed he's not gonna survive this. So he's stopping chemo and is just gonna die... His doctor is giving him a out 3-6 months. And how he's taking this is just disturbing... It's funny to him. He's laughed about it. He has started talking about planning his funeral and said "How many people get to plan their own funeral?" I've been trying to be supportive and so has his mom and I think him planning his funeral with her is what's helping her come to terms with everything. His mom forced us to go shopping for a tux and when an associate ask did he need a tux for a dance or something he just said "Nope. I'm dying and my mom is doing open casket". He told his mom he doesn't even want to be buried in a suit. His exact words were actually "Mom you damn well I don't want to be buried in a fucking suit". He cusses A LOT more since he's stopped chemo. But he said he wants to be buried in his favorite clothes and doesn't want to seem fake and wants to be the real him in his casket. He's been going through his stuff and figuring out what he wants to do with it all. I don't know how I feel about him cheating his death like it's nothing but a prom he's planning for. I get this is how he's coping but I tried asking what does he want to do before he dies and try to take him to do those but he said he just doesn't want to die but he knows he will and that he doesn't want to do some bucket list on things he wants to do before he dies. Instead he made a list of things he will never get to do. Like get married. Get a bachelor's degree, etc. I have no idea how that makes him feel better. Then he made a list of things he's already done with his life before he got sick which isn't much but he's happy with it. U know I can't tell him how to handle his own death but this is a lot. He's wanting the song cancer by MCR played at his funeral? It's like his death is a joke!