I imagine that all of us are reading this and feeling sympathy for you. People without pets/those who aren't "bonded" with their pets often struggle to understand this it seems.
6 years is a long time to have something. Even if he couldn't talk, he still showed emotion, he still had needs, and he was obviously a big part of your life.
I hope that you find a way to ease the pain together with friends, family or with counselling. I found that once my family and I had got over the initial heartache of losing Moofy we started being able to talk about him again, and although there are still many tears, we're often smiling at the same time thinking about how wonderful he was.
Wishing the best for you, and many hugs xxx