One time, pre-relationship, Mel and Langdon are playfighting (perhaps some ren fair crap), and Langdon pins Mel down and demands she surrender. Mel tries to playfully struggle free, and then actually tries very hard, only to realize that she can't, and that he could do anything he wanted to to her and there's nothing she could do to stop it.
That realization turns her on more than anything ever has before.
i like that u pointed out that this is pre-relationship so everyone knows mel realizes this while he's married. that's so important.
in my head, they just like to roughhouse since it's just their bodies trying to stay as close as possible. frank tackles her to the ground quite a lot and mel scratches/bites him hard enough to leave marks for days. they get rough with each other cause they're so comfortable around each other! and they tell everyone that!
but one day when mel does the tackling, he gives a few minutes before he flips her over and pins her to the ground. her wrists under his palm above her head and her legs trapped between his. he fully boxed her in and mel is squirming, writhing, struggling to break free but he has her trapped. frank tells her "there's no use, king. you're stuck with me" which doesn't do much to her until mel realizes his other hand is free to roam her body (it already is).
mel squeaks when he runs his hand over her peaked nipple (can he feel that though her scrubs?!) she knows she's safe and protected, frank would never hurt her. that doesn't mean mel can't wish he would. he's over her telling her to surrender, let him win, let him conquer, and her mind blanks when he leans in to whisper "or keep at it. i like watching you squirm." that does her in.
frank could so easily take something from her right now, he could so easily push his hand inside of her, so easily make her scream his name until he was satisfied, and that gets mel going. her hips involuntarily rock and when he notices, he adjusts them so he can put a leg between her thighs and let her get off.
he still has her pinned, completely in control of her, fully capable of doing something that will wreck his vows, and mel thinks it's so hot. she wants him to just read her mind and figure out exactly what she wants then push her beyond those limits - like he does in the trauma rooms. mel wants him to take take take while she's helplessly squirming around!!!!
and hey, this way, mel can say she didn't intentionally homewreck.