In the Season 3 episode “Green Light,” Saul tells Walt that he caught his second wife screwing his stepdad, which means Kim would end up cheating on Jimmy, and Kim just doesn’t seem like that kind of woman.
Especially when it involves Jimmy’s stepdad, who also hasn’t been introduced yet within this universe.
Vince Gilligan spoke with Screenrant for Breaking Bad’s tenth anniversary, and his words will almost certainly cause fans to envision a future where Saul and Kim can finally lower their guards and become a couple, but that might actually be the worst scenario possible.