First time & Martha

I haven't read the book but I heard there are some differences between it and the movie.

So in the movie they almost had sex with each other but got interrupted while in the book they went all the way. Why change that? The movie makes it seems as if Allie remained virgin till she got back with Noah again, while he just went out with other girls (not sure if it was only Martha) to release his build up frustration. No bashing of course, they were broken up so each did whatever they wanted, fair play.

Now, I'm curious about the relationship between Noah and Martha. Like, did they have sex in that dream house? Or was it just in her house? Because that was the only house where he was living in and surely Martha was inside there. I wonder how much Noah was capable of distancing himself when he was having sex with her, with all his grand love for Allie and all these years waiting for her.