I am so sorry about your loss. It is never easy to lose a much loved pet. She lived to be 22!! Amazing.
I am sure she is now an
watching you and guiding you.
As for your boy please, before you do anything else, take him to the vet for a thorough checkup. He is at the age where male cats, depending on their diet, could be developing crystals, stones, or other health issues. It may have to do with his mate's passing but please do not put it down 100% as that.
Has anything else changed since her passing? Have you changed foods, litter box location, sizes of boxes, litter brand, any and/or all of those things could lead to the issues you are seeing now.
Good luck and please let us know how everything is progressing.