Why is he acting like we are married?

so I have been hanging out with this guys and we both confessed that we love each other but agreed to keep things casual for some time.

lately, he has been acting like we are married or asks when we are going to get married. at first I thought he was joking but it has become a constant "joke". for instance, when we are cuddling he asks "when are we going to get married". or for instance we had a little fight the other day and he goes "are we getting divorced?". these are some of the examples, he does a dozen of these jokes and I do not get whether he is hinting at something or he is straight up stupid.

I just thought maybe our relationship reminds him of marriage because it is a little stagnant but I would love to hear your thoughts.
Why is he acting like we are married?
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