If Morgan finds out think how he will feel, he was dissappointed to be last to know about dating Jill again.
Imagine if Ellie finds out, it's not just Devon & Chuck but Sarah too, fallout will be huge, she is big on no secrets and trust, can't get any bigger secret than what there hiding.
Whoever finds out, I hope they explain everything, from the minute he opened Bryce's e-mail, to Sarah's role or maybe keep Sarah & Casey out of it.
Then there's also Dad, the connections are endless.