pawnbroker stold my 2 carat Tiffany Diamond, Heart broken

I just felt there is no use and I must except the loss and get over it.

Your agreement to sell him the ring supercedes any any agreement you made at the onset.

I am puzzled why this was not addressed at the time you noticed the diamond was missing. Your selling the ring to him implies a taciturn acceptance of the transactions that took place.
This sentence puzzles me---After my mom passed we planned on moving out of the area and I knew I had to do something before I left to deal with the theft of my diamond but I also felt I would not get much support after all I should have never taken it to a pawn shop to begin with. -pawn shops are not illegal--you would have had the support of the police and legal system behind you.

A man that commits crimes like this FEELS no guilt. I don't understand "........gives him more control of the situation".............

I've kept records and can have the jeweler that designed make a statement to the fact that the center stone was not the one he put in originally. This may be true, but that doesn't mean you can prove that the stone was in the ring when you TOOK it to the pawn shop and even if it was, you cannot prove it was not returned to you with the stone in it (in other words, he could argue YOU replaced the stone after he returned it to you)...........and sadly, the fact you let the matter slide for so long gives credence to the possibility that he did return it to you as it was originally, and at some point after that YOU replaced the stone.

Note--I am not suggesting this is what you did. I am pointing out that the law is about what you can PROVE. Proving he did this given this lapse of time is impossible.
You have no legal recourse now---the ring is in his possession.

Sorry for your loss.