Hello Susan, I'm Dr. Deb. I believe I answered a previous question about Sammy earlier this year.
I recently came online and see that your question about Sammy hasn't been answered. I'm so sorry that you've had to wait for a response,but if you still need assistance, I'd like to help if I can.
I'm so sorry that your other cat was attacked several weeks ago; I'm certain that this was traumatic for everyone in the family.
I don't doubt that Sammy was also traumatized by the event, especially if he's a sensitive cat, but my fear is that the stress of this trauma has triggered some underlying condition which he may have been able to mask.
This is a very common occurrence in cats and I see it all the time: they have a condition with which they're able to cope until a stressor pushes them over the edge and the condition basically catches up with them. I believe I suggested such a possibility when he was starting to act differently earlier this year.
If he had only been inappetant for a few days or possibly a week of so, then I might not be too concerned. But for him to still not be eating normally after nine weeks is somewhat unusual and a little concerning.
If you don't think it would further traumatize him, a vet visit with a thorough exam and blood work would be prudent. I'd want to rule out issues with his kidneys in particular as well as problems with his pancreas and liver.
If this is not a feasible option at this time (for whatever reason), then you could ask your vet about appetite stimulants such as Mirtazapine or Cyproheptadine. These drugs don't work in every case but they frequently can help to increase the appetite. Unfortunately, there won't be any over the counter options which can help to increase his appetite.
On the off chance that he's feeling a little nauseous (which is why he's not wanting to eat as much), even though he's not actively vomiting, he can be given Pepcid AC, 1/4th of a 10 mg tablet twice a day.
If he's less nauseous, then his appetite may return.
If he's turning his nose up at tuna and chicken, then I have to think that there may be something else going on with him and that the traumatic event was just the trigger but not the entire problem.
I hope this helps although I'm sorry for the delayed reply. Deb