In the beginning, Sal tells us that, "Mr. Winterbottom was playing the role of Father, with capital F. He sat at the head of the table with his white shirt cuffs rolled back neatly. He still wore his red-and-blue-striped tie. His expression was serious, his voice was deep, and his words were clear" (6.11). Honestly, he does not sound like a barrel full of laughs.
He treats his wife very much in the same way that his daughters (Phoebe and Prudence) treat her, which is to say, he totally ignores her. He doesn't really respond to her questions or ask her how she is doing. He doesn't thank her for the food that she cooks or for all that she does for the family.
Over time, though, we watch Mr. Winterbottom crack as he realizes that his wife has left him, and that he has lost something dear.
Once again, Sal the Great Observer, gives us a glimpse into what Mr. Winterbottom might be going through:
I thought about Mr. Winterbottom crying. That was the saddest thing. It was sadder than seeing my own father cry, because my father is the sort of person you expect might cry if he was terribly upset. But I had never, ever, expected Mr. Winterbottom—stiff Mr. Winterbottom—to cry. It was the first time I realized that he actually cared about Mrs. Winterbottom. (30.59)
Of course, Mr. Winterbottom is quite shocked when his wife finally returns home, bringing Mike the Lunatic, her long lost son, with her. But the best part is, he doesn't kick them out of the house screaming. Once he recovers from his initial shock, he shakes Mike's hand and tells him, "I did always think a son would be a nice addition to this family" (39.51). Not a bad guy, after all.