Although it is painful to watch and its impact never really seems to lessen every time I watch it, I feel that the scene where Lee slaps Amanda is probably one of the most powerful moments in the entire four seasons. It takes SMK out of its comfort zone – albeit briefly – and confronts us with the realisation that Lee could – and in this case does – slap Amanda. If you look, you can see him glance at Jack Harris as though he’s making sure he’s taking the whole scene in, only, in the next moment, to get too carried away with his cover and slap her. Amanda’s horror and absolute hurt are palpable, just as Lee’s own shock is. They are both left completely devastated by his actions. From the remorse on his face, I don’t think it was Lee’s actual intention to actually slap her as he did – and certainly not so forcefully. He started out by patting her face (although quite firmly when you look at it) as if he were trying to emphasise his frustration of having time on his hands for Jack’s benefit.
Realising the magnitude of what he has done, Lee immediately apologises, reaching out to Amanda automatically, desperate to connect with her again, his hands resting on her arms, but Amanda is far too hurt and upset to be receptive to such a gesture. She clearly doesn’t want to be near him. Her “You can move your hand” shows just how little she wants any physical contact with him.
When she walks away Lee runs after her – his thoughts no doubt centred on the fact that he could ruin everything with her because of his behaviour. He stands to lose so much and I think that alone propels him to the door Amanda is heading towards, needing to stop her before she’s gone. His “No! No!” is pretty desperate and anguished.
“It’s all right. It didn’t hurt,” Amanda tells him rather too calmly, trying to brush it all aside and probably just wishing to get out of there and not go into it all.
“I hit you.” Lee’s self-loathing is very marked. It’s as though he still can’t believe he could actually do such a thing to her, yet he is also still having to play his cover which makes everything all the more difficult. He certainly can’t apologise the way he probably wishes to – at least not while they are being watched by Jack Harris – lest he gives himself away completely. So he presses on, even though his words are hardly any comfort, trying to make it plain to Amanda that she should stay well clear of him. “You’ve just got to stay away from me. You’ve seen what I’ve been like lately, what I’m going through. I’m poison at the Agency.”
“I was only trying to help you.”
“Then let me make it easier for you. Just don’t help!” The words are harsh and uncompromising and he must know that they will add to the sense of devastation she’s already feeling. He certainly doesn’t hang around long enough to find out because he turns away to stumble back to the bar and Jack Harris.
Perhaps knowing exactly what emotions will be etched on her face, Lee doesn’t even look back as he goes. He can’t afford to if he is to continue with his cover. He leaves Amanda alone and utterly bereft; her eyes reflecting the pain she feels. When she raises her head to follow his progress to the bar, you can see the sadness and disbelief that haunt her. Yet she doesn’t try to go after him or speak to him again – he’s, after all, made it perfectly clear that she should keep her distance. Instead, she makes a bid to compose herself a little before heading out of the door.
At this point, they seem to be more distant than they ever have been. Even though we know that Lee is acting out a cover, at this point in time we have no real idea that Amanda has (or will very shortly) begun to figure it out for herself. After all, he may have a temper sometimes and has, on occasion, hurt her with his words, but he has never done something like that to her before.
Scarecrow & Mrs King - Getting to Know You 
This episode marks the point where Amanda’s trust and forgiveness is so unexpected that Lee’s eyes are finally opened to the precious treasure she is and he lets her into his life … forever.