PET scans are notorious for false positives, (especially soon after treatments end) and I am a person that has had it happen several times. I had a very hot node in my lung that the docs were sure was a met of the cancer. It turned out that the area was a very significant infection. I had/have significant aspiration issues from my treatments and chronically develop pneumonia in my lungs from this as fluids end up in them. What I had is referred to as silent aspiration, as the patient does not even realize that a portion of what they are swallowing ends up where it shouldn't, and there is no sensation that tells you it is happening. It only happens with liquids not solids. Never the less, I had nodes next to that area that they were equally confident were a spread of the cancer from the lung... not true. Just nodes doing what they were designed to do -eliminate the by products of the infection.

Please get a second reading/opinion. While mets to the lungs are not uncommon, their might be alternate explanations. My second opinion did a CT guided biopsy of the area in question to reveal the actual situation.

Lastly, especially now with this new issue since your original posting, mental state is an important issue, I and many here have been on anti depressants during our recovery. They take a while to kick in, as much as a month, but they may put him in a better frame of mind while all this is sorted through. These combined with good personal counseling may be helpful now.