I believe your statement is valid, you just need to analyze some situations to prove it.
I think you need to take a look at each character and how they act based on their perceived realities. This shows their complete commitment to what they think is real.
Gatsby for example, completely ignores the fact that Daisy committed vehicular manslaughter. He shows no compassion whatsoever for the victim. He percieved that this would be difficult for Daisy or that Tom would treat her terribly because of what happened. Thus, he determines to spy on them and make sure Tom doesn't beat her or something. Based on what really happened, someone who had an accurate grasp of reality would be afraid that this car would be traced back to him and it's time to get out of town so he didn't get caught, or if there was real guilt, he would stick around and be glad to confess or act as a witness.
Tom takes a chapter and a half to realize that he is not the only one cheating in his marriage. When he does realize it, he is not okay with it. But for some reason his affair was an acceptable option. This isn't fair. He therefore believes that reality means its okay for men to cheat, but not women. This is not reality because every man needs a woman to cheat.
I think you can do the same with Daisy's avoidance of the fact that Tom is having an affair...