Hi Chris, sorry to hear about your experience.
Like you I have had RT and am now on continuing HT. Post-RT it's been difficult with the emotional side of things - at times I have felt that I'm at the bottom of a very deep, very dark hole.
Separating out cause and effect ain't easy - is it the PCa?, the fatigue of having RT?, the stuff that goes with HT?, or re-assessing my life with the knowledge of reduced life expectancy? I still haven't worked this out (apart from knowing I hate the side-effects of HT)
I live a fairly socially isolated life and some of the things that have worked for me also help in this regard. I have been on an "Active Beyond Cancer" course (health advice and exercise) and this has led into an blokes-get-fit weekly meetup. Also a Tai chi course and a mindfulness course. I really value both the exercise and the mindfulness (I am amazed by that!) The Tai chi got a bit weird for me: but some things work and others don't.
My pathways into this have been leaflets at hospital, Macmillan centre visit, local PCa support group, council leisure / activity programme.
I have also accessed Macmillan counselling - I needed much more than the initial six weeks and I'll be ever grateful to Macmillan and my counsellor - it really helped. Maybe, if you feel it works for you, you could go back and ask for more? Also, I would echo Lyn's comment re Maggie's and so on.
Best wishes to you.
Steve