At your iPhone's date and time settings set the time several hours into the future. If you now return to the game and look at your Energy Meter you will notice that your Energy has been restored. Go back to the iPhone settings and set the time back to the correct time and when you return to the game you will have a replenished Energy Meter.
Wow
You could actually flirt with a guy even when you have a bf, it saves a lot of money without breaking up.