That isn't the problem. At least he can always trust Jiang Cheng to find something to think he's doing wrong. It's easier when he doesn't have to think up all of his own excuses and lies.
"If I don't need to use it any more, then I won't. It was worth it to take out Wen Ruohan. That means that Uncle Jiang and Madam Yu are alive and will stay that way this time. Lotus Pier and Cloud Recesses aren't going to burn. Whatever harm I did to myself is hardly comparable to that. There's nothing else at that scale I have to do."
The question is whether or not he'll need to use it any more.
Jiang Cheng's questions about the golden core have made him wonder. What if those torn pieces of his spirit did come back with him. What if he is unable to form a golden core in this new timeline? Can he stand to live as mundane? He would either need to find a way to use demonic cultivation to mimic regular cultivation, or else vanish into the mundane world before it could be found out.
Worse, what if the broken pieces remain in this body? He can't let Jiang Cheng swap into a body without the capacity for cultivation. That doesn't seem likely, admittedly - if the inability to form a new core were to have come with him, it likely will do so again. On the other hand, what if he is just tainted, and any new body becomes so, potentially leaving them both ruined?
He will have to be very sure before trying anything. Wei Wuxian will figure it out.