My boyfriend just told me wants to join the military

My and my boyfriend are both 17 and are going to run 18 in the summer. We’re just 30 days away from graduation and he just told me he wants to join the military. This is honestly out of the blue and he’s never said ANYTHING about this topic. I literally cried so hard because I know he’s the one I want to spend the rest of my life with. I want to support him but tell him not to at the same time.