It's called the Time Traveler's Wife, and is starring Eric Bana (yum) and Rachel McAdams. The movie is based on a novel written by Audrey Niffenegger and is far and away the best book I've read in the past year (and yes, I've read more than one book in the past year.)
Basically Henry has some sort of nerve condition that allows him to travel through time. Despite this abnormality, he manages to sustain a relationship with Clare, and from there all bets are off. It's an absolute masterpiece, and if you take any book recommendation from me ever, please for the love of God let it be this one. I don't know how Niffenegger came up with the plot, but it is so intricate and so tight that as soon as I finished it I wanted to pick it up and start it right over again. Seriously people. This book is amazing.
