You have not known pain until you have to try to help someone understand that their parents can't come visit today, and know that you will have to do it again tomorrow. And the next day. You have not known pain until you have to explain who you are over and over, and no that it does no good and that you can be of no comfort to your loved one - knowing that you are confusing them and upsetting them when you try to help calm them. But nothing calms them.
If this man can be happy for even one moment with his new love, and not spend his final days sobbing, wondering why he has been abandoned, then that is what should happen. And the fact that family members are gracious and loving about it is wonderful.
No one has the right to question this family or their decisions.
Bless you.