missed opportunity
Other than that ridiculous final episode, they never really had a great scene or episode with a connection between Darlene and Mark.
Maybe like Darlene's car breaking down on the way to Chicago. Dan is going thru something so Mark decides to not tell him and goes to help her instead.
Darlene finally admits that he is a good husband to Becky and not a bad guy. She thanks him for helping her. Mark tells her 'like it or not I'm family. Besides what was I going to do, send David to help you?' They both have a big laugh.