It's "complicated," the biggest lame excuse in the world next to "it just happenned."
No, Don and Sylvia. It didn't just happen.
They wised up, then they chose to be unwise. Having sex at her apartment when her husband could walk in any time if his work schedule changed, was begging lightning to strike. What I can picture is Sally bringing home guys in vans with long hair and disprespectful attitudes and just daring
Don to call her on her behavior.