True, but that doubt was still always there for Tyrion, even when he acknowledges it. I think he preferred to ignore that doubt and live with the fantasy that she loved him.
But regardless, it's still completely opposite of how show-Shae is playing out. It seems like the showrunners are trying to use Tyrion's marriage to Sansa as the reason for her betrayal, and that's a pretty crap adaptation.
ASOS
It's a bit premature to say it's crap when they haven't even showed how she'll betray him or why, you're assuming they changed one part of the story but will keep the rest identical.
Regarding Theon...
I really wish they had kept him off the entire season. Screw keeping the actor on board, you tell his agent that he can either come back in a year, or that they'll just recast him. If they get the actor back, fine, show the torture, if not, do the nice mind screw with the audience and introduce it old, beaten man in season 4 or 5.
ADWD
That would completely ruin the character. They have to show him being broken for Reek to make any impact on TV.