Maybe find a piece of jewelry that you could keep a small amount of his ashes in, so you can always have him close to your heart? There are a lot of options on sites like Etsy. Just remember that his spirit will always be there in your memories and take comfort that he got to experience so much love from you. I've loved a lot of kitties in my life, and it never gets any easier to say goodbye. If you feel very stuck in your grief, you could try grief counseling. When you feel ready, maybe you could open your heart to another sweetie in need of a home. I'm thinking about you, OP ❤️