I think Snow is depressed because she still has her heart. If she didn’t have a heart, then she wouldn’t feel bad about what she did. I think Snow may go to Regina and ask her to take her heart because she can’t bear what she did. Regina would then be in the process of taking Snow’s heart when she realises that Snow would suffer more if she has to live with the guilt of what she did.
As for the empty hearted curse, it makes me think back to Belle’s line to Rumple in Skin Deep “All you’ll have is an empty heart and a chipped cup”. Something makes me think that Rumple is going to have some involvement with the empty hearted curse. Whether that be just putting the idea into Regina’s head or something more remains to be seen.
All magic comes with a price!
Keeper of Felix