Why does grieving always hurt so much?

So....I'm studying grieving....Generally, it's associated with someone's death, but my grieving is over the demise of my beloved wife. She's still with me. The call it "artificial grieving...." which is kind of insulting. But....there are various stages of grieving that don't follow any particular order. If you'd care too, you can google stages of grieving and see what I mean. One famous person said that given a choice of grieving or nothing, he'd take grieving. I would prefer nothing....