Well I don't have the exact reference but this was cited in an article in New Scientist
a few months back.
Someone did a study around optimism and relationship breakup
to wit they asked participants (all of whose relationship's had recently broken up how long do you think it will take to get over it? then did a follow up to see how long it actually took.
What they found was that people consistently over estimated the amount of time they thought it would take (usually by fairly considerable amounts) to get over it as well as how much pain they thought they would suffer.
So not only does time heal but it does so quicker that you think.