Poor Frankie. She actually did have the potential to be a very tragic character, yet the way how she was portrayed/written (and, let's face it, acted) made it too hard for that.
That's always the angle I go for whenever I do a rewrite of the character (along with always renaming her "Helen"). If you think about the timeline of events (as well as the ages of all the characters and whatnot), she would have been a mere teenager when she eloped with Phillip, who then almost immediately enlisted in the army, and from what I've read, soldiers had to serve for at least one year before they could go home on leave. So that's one year alone in the Colby mansion... with Jason, who would have been significantly older than his teenage sister-in-law. If anything, Frankie/Helen could *potentially* be forgiven for the affair, on account of how young, vulnerable and lonely she was; but Jason... nah, man. You are *way* too old to be making a decision as stupid as that.
And then Phillip returns, and his wife tries to make up for her affair by having sex with him as often as they can before he has to leave again... and after finding out that she's pregnant, her husband goes MIA. At first, Frankie/Helen assumes that her unborn child is Phillip's; after all, they had sex way more times, it *had* to be his child. Seven years later, Phillip is officially pronounced legally dead, and the family holds a memorial service for him...
...only for afterwards, brother-in-law Cecil reveals that Phillip sent him a letter before he went missing... one that detailed that a medical test confirmed that Phillip was sterile... and thus, not the father of Frankie/Helen's son, Jeff/Geoff.
Immediately, Helen knows who Geoff's father is: Jason... who is, by this time, happily married to Helen's own sister, with whom they also have a beautiful set of twins. If this got out... it would destroy the entire family... *especially* Sable. And so, Helen leaves not so much so that Geoff can be raised as a Colby, but so that her dear sister's life won't be ruined.
Of course, it becomes much more difficult to keep Helen/Frankie sympathetic once we get to the actual main storyline when she returns 20+ years later. I could never buy Jason pining for her for all those years. Honestly, how could one possibly do that when they're married to *SABLE* of all women?! Sable Colby was a freakin' goddess of a woman, so full of life and charm and spice and class, and she just adored her husband, practically worshipping the ground he walked on. How on EARTH do you make him stop drooling over her (like how he was when they first appeared on DYNASTY) and start fawning over Frankie? Especially when the showrunners seemed determined to make poor Katharine Ross (who was gorgeous in "Secrets of a Mother & Daughter" a mere 3 years prior) look so terrible?
And there were other issues, but I'm too lazy and tired to go over them.
