Why would boyfriends of 10 years lie about wanting to marry me?

I met him when I was 19, he was 30. I already had a son. Five years later we had a son. I would talk about marriage after we had him, and he said that we would get married. I ended up finding out recently that he told his mom he didn’t believe in marriage. She told me when we were in a car ride alone with our son going to an appointment.

Why would boyfriends of 10 years lie about wanting to marry me?
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