Tempest (Tempest #1) by Julie Cross
"The year is 2009. Nineteen-year-old Jackson Meyer is a normal guy… he’s in college, has a girlfriend… and he can travel back through time. But it’s not like the movies – nothing changes in the present after his jumps, there’s no space-time continuum issues or broken flux capacitors – it’s just harmless fun.That is… until the day strangers burst in on Jackson and his girlfriend, Holly, and during a struggle with Jackson, Holly is fatally shot. In his panic, Jackson jumps back two years to 2007, but this is not like his previous time jumps. Now he’s stuck in 2007 and can’t get back to the future.