Hi MCD
I don't come to this site very often (hence the late reply) but wanted to offer my best wishes to you both. Also, I wanted to offer a few perspectives on gettig the diagnosis and "processing" this. For me this has been intensely personal - my feelings a seem to be quite different to other men I have talked to (maybe because of my life history and how the PCa happened).
Firstly, the diagnosis was and wasn't a surprise - things like the "leaking" you mentioned, plus other things were being coped with by a really rather rubbish strategy of going "na na na ... I can't hear you body ... going to ignore you body". This and one of the the other things about me of trying to be "the strong one" in the relationship set me up for an awful lot of personal shame and guilt towards my partner. Add to this the poor prognosis from the first hospital visit, the undermining of self-image caused by the treatment, and that I'm not a person for admitting I need help and a downward mental spiral was going on.
Looking back it was pretty hellish as a time (at one point I was quite scared) but thanks to some specific help I came through it.
Maybe this has some similarities to your chap and maybe it doesn't. For example, for me it is easy to imagine the age gap would prey on my mind in his situation. Or maybe it's really different. Whatever the situation is inside him there maybe a few things that helped me that may be useful for you to know.
Another bit of information: when I did access mental health support I hid the fact from my wife: maybe that's a telling statement. I felt so bad in myself that I knew I needed help - but quite unable to tell my wife about what I was doing (but finally did so about six weeks later).
In those difficult days we did talk - sometimes good talks, sometimes less so. The first point is that what helped me most was knowing I was supported and that my partner was "there". She didn't need to being doing specific things - just being there and around and carrying on. I didn't need directive suggestions - things like "why don't you try / do this ..." are absolutely not the type of thing to get me talking (and talking has been a large part of getting cured). What helps much more is the type of interaction like - and this sounds a dreadful cliche - "how do you feel about that?". That allows me to express myself as much as I wish to at that time. So, that's the second point: using open rather than closed questions and comments and listening to the language one uses and what "works" at getting things discussed (there's a big difference for me between "what do you think is the best thing to do?" and "what do you feel is the best thing to do?").
I am afraid all the above is necessarily bloke-centered - and that it what I wanted to do, show that inside some men's heads (well mine) it can be difficult to for rubbish things to be processed and for feelings to get in and out.
Lastly, the above rather ignores what you are feeling and so on - on that score I hope you are getting the support you need and deserve also.
Once again, best wishes to you both.