In response to the above dream, I don't understand how watching pornography and jacking off to other women's bodies is any different than cheating on your girlfriend. Obviously the action wasn't taken, but in the brain, there isn't much difference. If you want to have sex with other women you see on the screen, you'll want to have sex with them even more when you see them in person.
Speaks to the appropriateness of monogamy for males (and maybe females) and/or how good of a fit your girlfriend is for you, assuming that if monogamy is right for you, the right woman would never have you think about cheating on her, in real life or in a dream.
Yes, yes you would. Only societal expectations make you think that you wouldn't. No matter how fit she is for your desires, you will get tired/bored/overwhelmed with her and will want to try something else. It's in our design, to reproduce with as many mates as possible.