I agree with what you have said Chillie, but would ad that what would really be different is if Lester and Sarah make love in front of Dan. Lester, really ripping into Dan's chest and gripping his heart in a tight fist. Sarah looks to Dan for a moment, but then licks her lips while breathing heavily -- out of her gaping mouth -- barely containing her lust and her love, both for Lester. She is completely enraptured by Lester and wanting to help him hurt Dan as she is so far gone to the so-called dark side, knowing that helping him cow Dan will make him happy. While they make love in front of Dan, Sarah can't help spewing Lester's poison, saying repeatedly, "you're a real man, Lester, a real man. You're a real man, Lester, a real man." She barely gets this out, not because of emotions still locked away for Dan and their daughters, but because of the overwhelming heat that is shared between the two adulterers.
I do have one more thing that comes up in my head, a lot, for some reason. Sarah goes to Lester's room, as he promised that she would. After closing and locking the door, telling Lester that she locked it because everything changed out there tonight, and she really doesn't want Dan to be able to interrupt them. Lester tells her that there is one more thing he wants before she can spend the night with him, again. She looks at him, puzzled, to say the least. He pulls out a small container of spackling and a putty knife and hands them to Sarah. "Fill the peep-hole," he tells her, "I'm tired of Dan always watching us, he's like a little perv, never getting up the nerve to touch you, but wants to watch you." She takes it and fills the hole.