What does it mean when your boyfriend refers to himself as your husband?

Me and my boyfriend have always had an understanding that neither of us wants to get married. I can't imagine going through another divorce. I am very happy with the way things are now. But yesterday we were talking and I was telling him about what someone said at work. I dont remember exactly but it wasn't significant. He asked, "Did you tell them your husband agreed with you?" I just looked at him and he asked it again. Then he caught himself and laughed. He apologized... I told him it was ok. I think he was embarrassed. I have never referred to him as husband and I never referred to myself as his wife. I just hope he isn't started think about us getting married.
What does it mean when your boyfriend refers to himself as your husband?
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