I think it was early January this year when they were
last seen together, and Josh was still
talking quite happily about her in the Ellen interview which was mid-January. It is indeed sad if this is true, because as someone else said, they did look very happy and in love in most of their pictures. And Josh always seemed to glow whenever he talked about her.
To be honest though, it wouldn't come as a complete shock if they had decided to call time on their relationship. I have wondered for a while now if they were on the same page regarding the future (ie. kids). If they are not, then yes, perhaps it is time for them to move on. Neither is getting any younger and sometimes there are deal-breakers in relationships which may have nothing to do with love.
Whatever the case, obviously I wish the best for Josh, both professionally and personally.