I don't know what to do💔

All my life I've been alone. I've been cheated on and dumped too many times to count and I haven't had any close friends throughout my middle school and high school years. I finally found someone who doesn't make me feel alone and makes me the happiest I've ever been. We're both in our senior year of high school. A couple days he comes to me and says he's going to enlist into the Marines instead of college. I feel heartbroken. I have three cousins who are deployed at the moment and I worry every day about them. I didn't think I'd have to do that for my own boyfriend. I have severe anxiety and he's always been my rock through various changes in my life so far. He would be going to boot camp which is 3 months at the same time I'd be moving into a dorm at college which creates a lot of stress for me to be moving to a new area with no people. I don't want to sound selfish at all, but I'm worried and I've tried everything to convince him that he should go to college first. I just want him to stay. What do I do? Or any tips to help me cope? I feel so heartbroken.