I am currently in that situation, and I can tell you it's a battle to keep the darkness away when you suddenly find yourself alone. I'm managing, with help, but not everyone can.
I also think that women have a harder time with this than men, possibly because maternal death in childbirth used to be so much more common. But this is just a guess. Certainly until it happens to you its not the sorts of things that you think about too much, and once it does happen you tend to speak to people who are going through the more acute phase of it since they are still actively processing it.
I have not dealt with such a change but have dealt with grief. Try to catch the sun rise. It is incredibly beautiful.
It will probably hurt because the instinct is to want to share the beauty to enjoy it. The good thing is that you can, with the version of your significant one you hold in your mind. I am serious, do catch the sun.
Grief hits in overpowering waves. Over time there is space between the waves. They will always be there but they become survivable.
All the best.