"Shouldn't the trust part come before the marriage part?" It's not like he is opposed to the idea but it is all very foreign to him. He already agreed to being Xingchen's partner and he has no regrets about that. He would gladly grow their cultivation together.

"If you want to get married, then we can get married. I'll walk by your side no matter what." He doesn't need a marriage to do that but if it will make Xingchen stay by his side forever and guide their souls towards being together even after they return to their deaths then it is worth it.