Before Sally told him about the cancer, she coerced him into going to Paris for a weekend. I think she might have done that because of the impending health crisis, wanting to spend some quality time with her
More and more, as the affair goes on, I think Kevin is getting colder and colder feet. He put Molly off until Sophie was done school but then decided, oh never mind. But when this came up, he scurried to stop Molly spilling the beans. Even selfish Molly can't argue with cancer. I bet Kevin feels the guilt, now! But when it comes down to it, Sally is his wife and though he might love Molly, he hasn't stopped loving Sally and with all their history, he'll stand by her and see her through this and probably realize where his priorities really are.
In the meantime, Molly is going to be at loose ends. This is a soap, the affair is bound to get out, as it's a standard Soap Opera Plot. I anticipate Ty, Molly and Kevin will conspire to keep the secret from Sally while she goes through treatment. Tyrone is going to be devastated but I think that he'll take Molly back eventually. Of course Sally'll find out. What will happen is anybody's guess. If I was Sally, no matter how vulnerable and ill I was, I'd chuck Kevin out on his ear. But that's me. This will probably take a few months to play out so this is all speculation.
How do you think this is all going to play out?