。
I have too much free time on my hands.
Literal
I [topic-は] free-time [object-を] am-at-a-loss-with.
暇をもてあます ('to have time hanging heavy, be at a loss for what to do with one's free time'). もてあます means 'to be unable to handle, have too much of.' ~ている marks the ongoing state. A vivid expression of boredom.