Greene made her romance with the Spider-Man: Turn Off the Dark star public last year (Dec11), but the pair has called it quits after 10 months together.
The actress, who has previously dated Joe Jonas and Kings of Leon bassist Jared Followill, recently admitted she finds it hard to make her love life a priority.
The couple's hectic work schedules appear to have got in the way of its budding romance, as a source tells UsMagazine.com, ""They are over... Reeve seems to be fine and it was just crazy with their schedules.""
A separate source hinted the split could be only temporary: ""She knows this is a pivotal time in her career. I wouldn't say I could never see them getting back together but right now they are doing their own thing.""