it's what hes wanted this whole time, and it's like his whole character, but i dont want andy to die
Yeah, honestly Andy's entire existence hinges on Fuuko. Without her, he'd simply be Undead. And if they defeat Sun and Luna, he would lose that as well, and thus having nothing. This has been the case ever since Fuuko had went into Andy's memories and changed his perception on life and death and gave him the understanding on souls. Like Andy told Ruin, he has only one rule and that's Fuuko and his entire world revolves around her. So if she forgets Andy, Andy may as well be dead since Fuuko had told him that people don't actually die as long as you remember them.
Also Luna stop trying to deter them, you, Sun, and Soul pretty much forced them to do this. Just accept your defeat with dignity and get the hell out of here.