A simple reply to this question is, I try to remember that I’m not.
I think there are many times, in the world, in your family even, when it feels likes the world continues turning and you are left standing still in your grief. You’re the only one feeling sad or angry. You’re the only one remembering them in that moment. That you are completely on your own in your grief. Now, while it is true that you will be the only one who knows exactly what you’re feeling -and anyone who tries to tell you that they know exactly what you’re feeling is doing your story a disservice- other people are grieving. Just maybe in their way, that looks different to yours.
One of the things grief seeks to do is isolate you, making you perceive yourself to be lonelier that you actually may be in reality. And one of its tricks is to make you feel like you are the only one grieving, the only one experiencing what you are.
It’s just not true, at any given time there will be people grieving all sorts of things all around you, and a real source of comfort might just be joining someone in their grief and sharing something of yours.
When I feel like I’m the only one grieving and I am about to throw a pity party for one, I try to remember that I won’t be the only one grieving, and invite someone over to help blow up some balloons and hang the bunting.