Ouch!! I know how you feel! Have they given you a time for your surgery? It really is the only option and it is very straight forward. Mostly done by keyhole althought sometimes they have to do normal surgery.Being overweight is associated with gallstones, however i believe the association is genetic rather than cause and effect so please don't beat yourself up over this.
A change in your diet is definately a good thing, i had to cut out all and i mean ALL fat from my diet - it was a bit of a nightmare, but everytime i ate even the tiniest amount of fat i was in agony. I lost four stone in eight weeks! of course i have put it all back on now!
I was scared shitless about the op too, but honestly, the risks are minimal. I went in the morning, had my op in the afternoon - stayed overnight. Went home next day to a house full of gastro enteriritis - that was worse than the surgery i can tell you. Recovery from the op was quick. I was back to normal within a week, sooner if i didnt get sick.
Before your op they will check things like your blood pressure, do an ecg, take bloods, all the minimise any anaesthetic risks. If they consider the risk too high, they wont do the op, simple as that.
The postive thing about it is, once you have had the op, you have no problems and no pain - beleive me, i was hospitalised three times with the pain and had to take morphine based pain killers, that is quite a relief!!
Try not to worry- easier said than done, but you will be fine xx