I'm so sorry. I understand how you feel. In february my chinchilla Kassy passed away unexpectedly from a blockage. I had no thoughts that she would have died, but a few hours later, she had.
For me I still had my male chinchilla so I put all my time thoughts and energy into him, although I think I was more sad from Kassys death after the initial shock for him because he was now alone.
You did great caring for Optimus! Dont doubt that ever. He had a excellent loving home with you and care that most chins don't recieve. and I know unexpected things happen but when you have only had them a short time and they are young it makes it more difficult.
Are you going to get him cremated? I did that with my chinchilla and hamster, they give you their ashes and their paw prints. Its really sweet, and then they will always be with you
Really it's just going to take time. I thought I would never get over Kassy being gone, or Haylee, but I have, for the most part. I still get teary thinking about them, but I know that they arent in pain or sick anymore, and thats what comforts me, and that I gave them a great home for the time that they were alive. If you have other pets maybe give them extra love to keep your mind a little occupied?
I am so sorry though, I know you are hurting, and it hurts me hearing about your little guy