This is probably pointless to ask because you seem determined to live in Fantasyland, but why would DD even have a "false" marriage? Why not stay single and play the field while sneaking around with his "true love"? Gillian was single part of the time after the show ended-they could have gotten together then! Maybe it's because the only ones who want this relationship are delusional fans!
There's a big difference between flirting with your co-star in front of 5000 fans who want to see it, and having an affair. And Ted Casablanca hasn't said anything of substance-he just hints and lets the snoggers go wild. DD and TL got married, had children, have declared their love in public, and gotten wedding ring tattoos on their 10th anniversary. But you snoggers can't accept that is the way adults behave who love each other, not sneaking around for 15 years while committed to other people. It's insulting to both DD and GA.
Maybe it's because the only ones who want this relationship are delusional fans!