i’m scared my cat is going to pass soon

this is Tigger. he is 15 years old. i am fearful. he has declined physically a lot. i know you can’t really tell from the picture but he is frail, skinny when he never has been, not eating well whatsoever. about a year ago we had a medical scare, he ate some form of foil and it really hurt his throat. he threw it up after our vet visit. after this he has just … withered away almost. he stopped eating well or at all some days, he doesn’t respond the way he used to, he hides away. he’s never been this way before. i know what is happening. i know he is going to pass. i don’t know what to do. i am scared to take him to the vet. i’ve spent thousands of dollars in the last year and a half helping him and i don’t know what to do. i don’t mind spending a few more thousands of dollars but i know it will not help him. i know what they are going to tell me. i don’t know how to let him go. i think i’m just venting now but any advice or a step by step on how to mourn would be great 😭