Cassian is as attentive and selfless a lover as he is a revolutionary, but he has a hard time being on the receiving end of that kind of thoroughness - the guy's got some self-worth issues from years of war trauma and is sort of subconsciously always trying to prove himself worthy of his partner's time.

Jyn asks to tie him up and then proceeds to kiss him and caress him and tell him how beautiful and good he is - and Cassian comes apart.