How do you leave him when he has terminal cancer? Somberly, but firmly. You don't owe anything to people who abuse you, not even friendship. Sucks for him to die alone, I guess, but he's the one who made this deathbed, now he's the one who's gotta lie in it, and if he has to do that alone and unloved, well, that's not your fault. If he wanted you to hold his hand as he died, he should've tried not abusing you.

Amy's advice being a bit subpar today, I offer instead Mantis' advice, which is to eat him and his wretched mother. Immediately.

Also, bonus comic.