Marrying for the benefits

I live with my mother, sister and brother in law because my brother in law got stationed to another state and my sister didn’t want to be alone while he was training. But now they’re divorcing so once I graduate school in 5 months we have to move out of the house since it’s technically my brother in laws. I told my boyfriend of nine months (who is army in ait) today that I’ll be moving back to my home state when I graduate unless I can afford to move out on my own even if it’s renting a little bedroom. But I don’t have a job yet but will be applying to places soon. He laughed at the idea of me being able to and said we should just get married for the housing allowance benefits then travel together to all the places he’ll get stationed. He’s been saying that a bunch during his whole hbl. Even to my mother and his family. Surely he can’t be serious? He said we wouldn’t even be engaged we’d just skip that step. But we’re both 18 so maybe I should tell to cut it out with that talk?