Don't be so hard on yourself - start off by just joining in and reducing your plate by 1/3 of what you normally would have eaten - all of the fun and little deprivation - HEY, it's a start! Then by 1/2 and/or try to modify some. Don't go cold-turkey on not eating anything with people - that's a good way to sabotage your efforts.
For example my husband and I would have each gotten appetizers with nour meals and today, we split a cup (yes, not a bowl) of chili as an appetizer - we had the flavor and a small portion of the calories.
Don't beat yourself up so bad. Just take wht you want and cut a third of it out and give it away or throw it away or save it for another day... but keep on going, it will get easier over time.
Las tnight the in-laws insisted on dessert for my brithday - so I ordered a slice of carrot cake (so the candle hing could be done) and I ate less than a 1/3 of it and took the rest home - all of the pleasure and none of the deprivation!