He doesn't protest, try to stop him or do anything except kiss back. After this many years, he knows when Huaisang actively wants something, it's best not to get in the way and it's not like he's averse to what's going on anyway. However, he does help Huaisang undress before backing him to the bed while kissing him again, hands finding his hips.

And it's Huaisang who lands on the bed first, Wanyin's mouth finding a spot on his neck to bite gently.