Yu Weimin really did what the system told him, not because he wanted to follow that thing in his head but because patient 1298 told him so. Their lives were so complicated that from start to finish, the two of them tortured and retaliated against one another.
But at this point, when he had already lost that person, none of those things mattered. Yu Weimin's heart had died with the man, and he started living his life as a corpse.
He confessed his crimes and even asked the authorities to give him the most severe punishment other than killing him, making it clear that he wanted to be tortured. In his heart, he felt like he hadn't paid back enough.
A life for a life—who does that? Who gave patient 1298 the authority to do that for him? Just why? They weren't lovers, and they definitely didn't have a great start, not even being friends. At most, they could be termed stranger enemies.