You're clearly enjoying Sigma's embarrassed expression, and for the best reason.

Luckily, both of you are alone in his office so nobody could witness how flushed he was, Sigma's pale face planted with red lip-shaped smears of red all over—some even trailing to his collarbone. You made yourself comfortable on his lap, as you press kiss mark after kiss mark on his face.

Although he seemed "annoyed", Sigma never pulled away and was deeply enjoying the endless kisses you laid upon his face.