Feral or stray cat tested FIV+

We recently trapped a stray or feral cat that we have been feeding for a few months. He was brought to the vet, in hopes of just being tested, neutered, flea and tick prevention, etc. But, he tested FIV+. We don’t know if he displayed any symptoms or discomfort as he went straight to the vet after trapping. Is euthanasia the right call? He would be a barn cat with exposure to other cats, and we don’t want to risk other cats being infected. The vet supported with this idea. We don’t know what to do