My fiancé is among those who can eat and eat without gaining weight and he has finally come to learn that he needs to support me in my endeavors (which has been a great help at home). The office on the other hand is a completely different situation. What I have done is this... I go to lunch with coworkers, but I generally just pick at the food then take the leftovers home to the endlessly eating man. When there are cakes and goodies (which there seem to be everyday), I grab a piece of whatever it is to socialize but then discard of it later. I know it seems wasteful, but I would rather have it in the trash than on my gorgeous hips! Good luck. It's always a struggle.
My best friend is considerably overweight and I have been trying to support her in her weight loss. What I have observed is this: 1) she feels guilty for having gained weight in the first place, which manifests as self-defeat; and 2) working out does not make her feel good yet... actually it makes her physically uncomfortable and frustrated. What has been working for her is lots and lots of love, support and reassurance. Find someone who will not let you do this all on your own. You need someone who really truly supports you and knows how to support you in a productive and positive way (I am personally not a fan of tough-love). This is hard for me too and I used to be a competitive athlete, don't beat yourself up over not feeling motivated every single moment but remind yourself that this is good for you and will feel better as you keep with it. Work on providing yourself with positive reinforcement (even just a five-minute mediation focused on loving yourself and the world around you helps). If the workout is too much for you to follow every day, take a day off from the program but do not take a day off from yourself. Use the time to take a walk, mop the floor, anything not seated... but keep going back to the program; having the guidance it provides is essential. Good luck! Lots of love and health!