quit smoking AND get in shape?

The holy grail. Can it be done? I have been quitting and starting smoking again for the past seven years. With my last quit I gained 14 kilos, and then promptly started smoking again! An quit and gained and started another 10 or so times. My body is a mess, as you can imagine. I have bullied myself into trying again for a final time and I am terrified. Any tips?