You can stay in one place and get on with your life - you just won't have him at your elbow on some occasions when you feel you might want him to be.
Lots of naval types do their own thing. It isn't as bad as other forces where there is generally a lot more moving about involved.
Most people decide on their partner first, rather than their lifestyle, tbh. He might not get in, anyway. Or he might join, hate it, leave, or join, and fail basic training, or join and decide after a year to pvr. There are no guarantees with this lifestyle.
What are your plans? Presumably you are studying something with a career in mind? Where will that take you?
And can I just say, I may have been a military spouse for some time (once I had finished serving myself) but I was never, ever, a WAG. Yuk. And despite that ridiculous forum, I've never know a military spouse describe themselves as one. Horrible.
At 21, you have a lot of decisions to make. If you want to be with him, then there's always a way round it. But realistically, you need to be thinking about what YOU want to DO, not what you don't want to do, or what you don't want HIM to do.
What Do you want to do??? It's all a bit negative for my taste. Try concentrating on what you are going to do after Uni. Which jobs are you going after? Are you staying in your uni town? Moving to the big smoke? Looking for a job in a rural area? Where will your career take you? Is it portable? Is it trying in that will involve working for one company for ever until you make partner? Or is it something that is done on a contract basis and involves you working independently and making a name and career for yourself as an individual?
And to shove this in AIBU smacks of grandstanding. Anyone would think you just wanted a whole bunch of folk to yell LTB to validate your cold feet, rather than discussing it sensibly with a bunch of women living it.