I'm not sure how far the translation is up to now, but right at around chapter ~90 or so, Shen Wei manages to get the promise out of Zhao Yunlan that they would die together. It's the culmination of Shen Wei's plotting --- that he's calculated and tricked ZYL to feel guilty enough to die with him (when the great seal goes he goes, and the seal is GOING), but then ZYL in the end just went, "sure I'd die with you. Will I live long enough to bury my parents?"

Then right at the end of chapter 105, SW changes his mind and fullfils his character-arc (no death no extingishment no godhood) instead, by choosing to be self-sacrificial without taking ZYL with him. Not only that, SW tried to wipe all of ZYL's memories of him before throwing himself into the flames. So when SW didn't die but is instead in a way instantly reborn, ZYL is at first worried about when he's going to wake up, and then secondly, FURIOUS that SW would have the gall to 1) break their promise to die together 2) brain-wipe him.

So SW is apologising to make ZYL feel better, but he's not saying anything specific because if he had to choose he'd do the same thing over again.