I am so sorry for the loss of your beloved son Cooper! I can empathaize with what you are experiencing as my son Joseph, who would have turned 18 in March, was born prematurely and died after only living for one hour. The pain from that was something I would not wish on my worst enemy, and I did not understand God's plan at the time, but now looking back eighteen years, while the pain is less, although it will never be completely gone, I believe I do understand now why he chose to make Joseph one of his angels. Thus I hope that knowing that your son Cooper is now in God's loving arms and is one of his angels that will bring you some comfort.
Below is a poem that was given to me after I lost my son Joseph that helped in my healing and closure process and I pray that it will help you both in yours.