Jena - please, please don't think that this has anything to do with you, what you did or how you handled the situation! You sound like an incredibly caring person and you didn't deserve this to happen to you, twice.
If the pet store couldn't even tell if the bird was weaned, needed to be hand fed, or what his overal status was before they let him go - it is their fault, not yours. Please don't blame yourself.
The tragic, sad part is that you are attached to that little guy and you've invested your emotions - I don't want to sound harsh by saying this - but I believe that the pet store has taken total advantage of you and your willingness to trust them.
Please know that I am here for you - if you need to rant, vent - whatever...
Again, I am so, so sorry that you have to go through this!
Please keep us posted....
It just all sounds so unfair.