If the ME/CFS-triggering virus he likely caught was anything like mine, the depression and anxiety may have been worse than any of the ME/CFS symptoms he was suffering from, in terms of causing suicidal ideation.
My virus triggered anxiety, depression, anhedonia and blunted affect in myself and in a few others who caught the same virus. Only later did this virus appear to trigger my ME/CFS. I find my ME/CFS symptoms themselves don't induce suicidal ideation (although I am fortunate enough not to suffer from horrible ME/CFS symptoms like muscle pain or migraines); but I find the depression and anhedonia certainly do.
Medical science has been far too slow to appreciate the role that contracting a chronic infection can have on health status. When people are fine one minute, and the next minute they are inexplicably suffering from severe anxiety, depression or dysphoria (without any good reason in their life for this to occur), then I think infection should be suspected and investigated. But this investigation very rarely happens.
It makes no sense that someone can be perfectly healthy mentally and physically, and then without any obvious reason, all of a sudden start suffering from anxiety or depression. Scientific explanations are based on uncovering cause and effect, and so when there is a sudden inexplicable mental or physical health status change, there must be a cause. The acquisition of a new virus or bacterium in the body is, in my view, a good candidate to explain such sudden health status changes.