I share your grief. Late in May I too went to the vet as two and left as one.
I had adopted Bear from a rescue where I volunteer a year earlier and he had never been 100% healthy, but I always believed we’d be able to find something that would cure him. He was 11-12ish when he entered my life and the same age when he died. The wound was greater than I’d ever expected given our short association, but I am blessed to still have my (currently 20 and 21 year old cats who’ve been with me almost their entire lives). Ironically I’d adopted old man Bear to be their new friend until THEY passed away.
You never know how long you will get with any one animal, but the way they change you and the way you change them makes all the heartache worth it. Best of luck with your new furbaby.