God, don't say it until he does. Definitely makes more trouble than it's worth, my girlfriend said it first, I responded awfully and it sprouted all sorts of issues that weren't resolved for months. So bad.
I think you should leave it until the dynamic has definitely shifted into one of those very close lovey dovey type relationships where it's blindingly obvious that he loves you back (but hasn't said it) before you say it. Or he'll say it first.