It wasn't that Spencer was trying to keep secrets per say, but if they didn't ask then why say. They were the best profilers in the FBI and if they couldn't see his ring and put together he was married then why did he need to tell them. Sure he was a mutant and had transfer from the mutant unit, but if they didn't ask then who was he to put the pieces together. It was the same for most things in his life; brothers, powers, and personality. But apparently these were things you are supposed to tell friends.