Will we ever see a scene or interaction between Franco and fellow artist Elizabeth? If he's been stalking Jason for a long time, then Franco must know the affair he had with Liz. Franco will go after her just to tick Jason off because even though he's with Sam right now, Jason will always care about Liz.
Or another scenario would be:
Liz takes a break from mommyhood for a couple of hours and attend Franco's art show. They meet and hit off right away because of their passion for art. Liz still loves Lucky but she is physically drawn to fellow artist Franco. After fighting her feelings, Liz caves in and decides to sleep with Franco.
TPTB could have written these storylines if they insist on writing the Liz character as an unfaithful wife. But nooooo, they paired her with her brother-in-law, which I think is downright disgusting.