At one time, Dave was a good, wholesome guy (despite his bad 80s glam-band hair).
But when he first appeared on the page, he was flat and boring. As a supporting character, he served no purpose other than to move the MC from the beginning of the story to the end.
He needed a life. So he developed one. (Well, I developed one for him.)
Of course, no one's life is ever perfect. Dave was no exception. His wife was bitter. She was too young when she got tied down with a kid, and she had a tendency to make Dave the victim of her venom. If she wasn't locking him out of the house or making him sleep on the couch, she was cheating on him.
Poor Dave. Poor, poor, pitiful Dave.
And shame on me for making his life such a drag, right?
Well don't waggle your finger at me just yet.
You see, Dave started to irritate me. Even though he had a life, he wasn't doing anything other than playing the role of World's Biggest Chump. And let's face it, nobody likes a chump.
So I started thinking. And thinking led to tinkering. And tinkering led to an interesting realization on my part: Just because a character is "one of the good guys" doesn't mean he (or she) can't have some serious flaws. In fact, giving a character shortcomings makes them A.) more believable; B.) more interesting; C.) more likable in the long run; and D.) more fun to write about.
It made a lot of sense for Dave to act like the north end of a southbound moose (kind of like you'd expect a guy in his position to act) and for his wife to respond to his behavior with bitterness and insecurity (allowing the reader to maintain a feeling of sympathy for him).
Not only did this make Dave a more intriguing character, it also gave him room to grow and change throughout the story. And that was something he had to do anyway.
After all, he is one of the good guys.