To be fair, I suppose it cannot be easy to be going through what
you're going through now, but forgive me for being blunt, marriage
is something that you shouldn't even consider at this point in
time(nevermind the 9 years, it still wouldn't be right even if you
had been together for 90 years if you two ever came to such
conclusions!).
As some have pointed out, there're so many possible reasons as to
why your bf feels the way he does - be it because he has fallen for
someone else, awakened to the reality that you're not the one he
wants to spend the rest of his life with(even if that has taken 9
years on his part to realise, but to be fair, these 9 years are
very special times in anyone's lives as people will invariably have
a change in mindset of goals in lives - which in turn would affect
the kind of partner they want - as they move from adolescence to
adulthood), or maybe, he is just bored with the sort of routine
you're going through and nothing more - and without knowing your bf
and you personally, it is indeed quite hard for anyone to advise
which category your bf falls under. Hence, I wouldn't like to
speculate on the reason for your bf feeling the way he does because
my guess would only be as good as yours...
Nevertheless, I suppose you ought to only change if you think what
he says makes sense(and you genuinely want to change) and not make
those changes exclusively for him because he wants it and you want
to salvage the relationship - it might work for the time being, but
there is absolutely nothing to safeguard your future(as you might
be tempted to think). If anything, it might actually be a cause of
contention later on in your relationship(whether you're married to
him or not) and might spark off more dissent. Basically, I don't
believe anyone should change himself/herself solely to accomodate
his/her partner - if anything, he should learn to accept you for
who you're and if he can't, then I think it might be better you let
this relationship go. As a last resort(and cruel as this may
sound), I think you'd be better off living with 9 years of a
relationship gone sour than a wrecked marriage that would haunt you
later on.
Then again, of course no one is in a better position to find out
why your bf has had this sudden change of heart than you - perhaps,
a heart-to-heart talk with him to iron things out might do wonders
if this was simply a case of him getting bored with the mundane
routine you've gotten up to for 9 years. At least, he has been
honest enough with you to tell you what he feels - and hopefully,
the chance he has provided for you two to work something out will
prove sufficient to salvage your relationship... 
