I should break up with him now because it'll be harder later on,
will it be harder to do this when there is a good reason to do it(no more good times because he is gone) than now when you are having fun? call me skeptical.
and that I might hold him back if he gets too attached to me.
him thinking you are holding him back is up to him to decide, and likewise leaving you because if it is as well. stay in your own lane
my issue is you are already planning on staying with him (as much as this can be called being with him) after he is gone, which seems stupid to me. I probably would not end a relationship today which was working for me today, that does not make sense to me.