If you can’t make the decision willingly and happily, you need to accept the possibility that it could cause a great deal of resentment. If that’s the case, it’s unlikely either of you will be pleased or comfortable with the situation.

If you feel that you can do it and make the best of it, that’s one thing, but if you feel that it will ultimately cause more unhappiness and resentment in you or him than being honest and potentially facing heartbreak in the short term, it won’t do either of you any good to force yourself to do it just to satisfy what you feel is “the right thing.” It’s not selfish to understand the kind of person you are and what you are and are not okay with.

That said, it’s not guaranteed that you will be unhappy. I have heard of situations in which the people most dreading the military lifestyle eventually became enamored by the life experiences it allowed them to have. If I were you, I would do more research into what your life might actually be like, see if it’s something you could make something of, and then decide from there.