I don't remember the name of the novel! It's a BL quick transmigration situation with 1v1. In one of the arcs the ML is transmigrated from an apocalypse world into a xianxia world and the MC's mission is to help (?) him. In the next arc, the MC goes to the ML's original apocalypse world and meets the ML pre-transmigration and then waits for the ML to 'go' and come back.
I think its 'The target always think that I like him' https://www.novelupdates.com/series/the-target-always-thinks-that-i-like-him/ What you mentioned is Arc 5 and 6