When you start asking this question.
simple, make it have a future!
How do you know you have no future?
Because your life plans are different?.....Is it beyound the realm of belife that your life plans could change....and so could thers?
Is that not what shareing your life with someone iis all about...not having ridged plans?
But finding a path and walking it together?
Well; I would normally say about a year or so ... BUT; since you are questioning the relationship .... probably about NOW for you ... especially IF you've tried to talk to him and ya' can't reach an agreement on your future ...
I'd give it 3 months, then move on.