I'm sorry you're feeling so down
You are not alone in feeling this way. I think everyone who is overweight on some level feels that once they reach their goal, all their problems will disappear (or at least the biggest one). I've certainly felt that way.
If your family or friends miss the "old you", then that's their problem, not yours. I hope that your family would be thrilled when you reach your goal, because it means that you can enjoy a long, healthy life with them!
As for your other concerns (getting to goal then failing and always feeling like the fat girl), I think these things will be a lifelong challenge. Try not to worry about the future- it distracts you from what you can do today to get to your goal.
You should be really proud of your accomplishments so far- you've lost a LOT of weight! You're amazing! You're allowed to have a down day- we all do- but don't forget the power of positive thinking