You're doing well Maria, naming the problem and facing the fear that keeps you stuck there are definitely the first steps in overcoming it.
I hear you about being scared of putting weight on but there's no reason why you should.

Being scared is horrid but the only way to get rid of fear is to do the thing you're scared of. It sounds back to front, but its the only way that works. Waiting for fear to go, so that you can do something, doesn't work, it leaves you trapped by the fear.
Doing what you're frightened of is the only way to beat it. You do it, through sheer willpower and all of a sudden, the fear has gone.

As for being happier once your eating disorder is gone, well that depends on lots of things. Its a bit like me saying I'll be happier when I'm slim.
Both things might help a bit, but real happiness comes from liking and accepting yourself - and that takes work if your self-esteem is damaged, as it seems it might be. You may need some counselling type help with this too, which you will also get at the OA group or you could see a counsellor separately.

Your metabolism will mend fast because you're young. Eating a sensible diet and exercising regularly but not obsessively will soon have it back to normal - this takes longer as you get older, so some of us wrinklies are having to work at this one - it shouldn't be too much of a problem for you.

You've got all the possibilities in the world ahead of you - good for you for setting out on your adult life by mending yourself and regaining your health. I wish you all the very best, you're a very brave girl, lots of love and hugs from across the Atlantic.
take care, Jay