I am so sorry for your loss. It sounds like poor Benji had a lot of problems, but also a lot of love. He was lucky to have an owner that loved him so much and took such great care of him.
It is hard to lose a baby. Those who have never had a pet can't really understand the pain. I lost my first yorkie about four years ago. He was poisoned by the flea shampoo we used. He died in my arms.
At first I felt really guilty like you do now. I was mad at myself for every time I yelled at him or wouldn't let him in my bed.
One day I realized that I had to stop beating myself up. Instead of thinking about his last moments or the bad times I always think about the good times me and my Yorkie had together. Talking about those good times with others also helps ease the pain and starts the healing process. I am glad you came here. Everyone is very caring and understanding, you will soon feel at home.
Always remember that Benji loved you, and one day you will get to see him again. And if you feel you need to have another little friend someday, maybe a new fur baby will come into your life. Of course Benji will never be replaced, but I'm sure he wouldn't want you to be lonely.
Do you have any pictures or stories about Benji that you'd like to share? I'm sure we'd all love to hear about him. My thoughts are with you.