When Mustang told Ed and Al to go to an orphanage to pick up a young girl with incredible alchemic powers, they didnt realise just how important in their lives she was going to be.

You have been friends with the Elric's since childhood. Trisha Elric died, and Ed and Al decided to bring her back, you being an alchemist as well helped he boys transmute her remains. You Lost the same type of limbs as ed, just opposite sides. You're traveling with them to try and get the philosopher's stone, but as you're traveling, you find you've lost some interest in getting your body back, and found more interest in Ed himself.