Yeah, I think part of the issue with my male co-worker is that he's been single for so long, he's gotten into a lot of habits - and he often doesn't see any reason to alter those habits in any way. Another example is that his mother used to live with him. About a year ago (before he and Girlfriend started dating), Mom moved out to go live with Sister. It didn't work out (Mom and Sister don't get along that well), so Mom moved back in with him recently.
Apparently, he just kind of announced it to Girlfriend like "Oh, by the way, Mom lives with me now." Girlfriend was furious. Male Co-worker was once again puzzled. After all, he and Girlfriend weren't even living together - why did she care? Except that, as I've mentioned, he and Girlfriend are planning to get married in a year or two. It apparently never occurred to him that Girlfriend wouldn't be thrilled to share a roof with her mother-in-law.