I'm so sorry, that is so rough.
You probably suffer from Major Depressive Disorder (Depression), which is why you are unable to get past your grief. I was diagnosed with the same thing when I was about your age, and it seems likely that is causing some of these issues, and making it impossible for you to move on. I know it probably doesn't feel like that, and I know you probably think this is how life is supposed to feel, but it is NOT. It DOES get better, I swear on it. You just need to get some help working through this.
There are absolutely bigger issues at play here than normal grief. It's time for you to see a psychiatrist and therapist, to work out what's going on. That's the only way, and it will take work, but you CAN be happy again.
I would also suggest getting another dog if you don't have one. Dogs can do wonders for people with certain Disorders, and your guy probably helped you stave off yours for a while.
Trust me, it gets better! Get some help to deal with this.