But how did he go from how he was before they were married (he certainly didn't seem to object to skin-baring clothes in her flashbacks) to the point where he doesn't even want her to open her top button?

That doesn't really surprise me so much. It's a jealousy thing. He didn't mind before they were married because she wasn't 'his'. But now that they are married and she is 'his,' he doesn't want any other man looking at her, so she has to stay covered up. It probably also has to do with propriety. A young, single girl can behave in a way that would not be considered appropriate for a married woman.