There could have been a few more tells than a speech about meaning what he says.
The director didn't wan't Gyllenhaal's prints on his wife's tits, obviously.

Christ that's retarded.
I understood what was going on perfectly. It wasn't hard. All that sex scenes would've added was sex scenes.
They didn't show any intimate scenes because they didn't need to.

I am a very well refined watcher of cinema in English so dont need your certificate thanks.

What are you, 13 years old? Why aren't you doing your school work?
Rene

is it coz Russo was his wife? He doesnt want her boning a good looking young man?

I think they made the decision based on
A. It didn't really needed to be shown, and it would have given more information on Lou which would have detracted from his mysterious nature
B. Leave some thing to our imagination like the hints that Lou is into some weird stuff
Or maybe you're correct and they felt it would make people uncomfortable however it's unlikely since this was not a movie to get comfy with.

I think they left it offscreen to make it more intense. The conversation between them at the restaurant impled that Lou was asking for things that she didnt want to do, so either he was abusive or into some weird stuff. Everyone's definition of what they consider extreme is going to be different, so its almost easier to leave it up to the audience's imagination to picture exactly what they could see Lou requesting that would upset her.

This movie plays on fine lines among observation, voyeurism, and intrusion. My hunger for their intimacy made me feel like Lou; the difference was wondering where my natural, human curiosity might manifest into something deprave. I wouldn't call Lou too human, however.

Stupid comment, especially your last sentence. How they performed in the bedroom would have nothing at all to do with Lou's story.
.... TxMike ....