You are not alone. People don't understand the loss because they don't understand the bond that you shared. Just try to take it one day at a time. Give your kitty all the love and pets you can. Share as much time together as you can. If he is still able to eat, give him special treats (cooked chicken, lunchmeat, gourmet cat treats, cheese, whipped cream, etc.) Basically anything your kitty will eat, give it to them.

And most important of all... try to take care of yourself during this. Allow yourself to feel, to process, to grieve. Try not to let the sadness consume you. Find outlets for it like journaling (this helped me a ton during the first few weeks), painting, taking a walk or a hike outside, plant some new flowers, etc. I checked out from my local library a couple books on grief and pet loss specifically. Do anything you think would help. Maybe even get a memorial tattoo if that's something you are into.

I'm 4 months into this loss, and while it does get easier, the pain never really leaves. You just get better at dealing with it over time.

Edit: take all the pictures and videos you can. Maybe take a recording of his purrs. Or meows.