He held back. Well. Sort of. Even though Faith was super strong and probably could have handled a fully energized, all over the top Sam while cuffed up, Sam didn't exactly want to risk hurting her in any way while doing all of this. She said she trusted him and he really was not going to put that trust at risk. Not ever, if he had anything to say about it. So while he was forceful, Sam wasn't going at her as roughly as he would have if she'd have had her arms free. He was more concerned about giving it to her good anyway. If this really was entirely about him, he wouldn't be double checking to make sure that he was doing things right. Which, at the moment, he currently was.
The declaration of love that he sent out in return was lost as Sam buried his mouth against hers. He hadn't held back on the teasing. After all of that, it only seemed right that he gave her what he'd been leading up to all along.