This is a very sad thread. I don't think the prostate cancer is the problem. I don't know what is.
You are welcome to post on here we are quite sympathetic and not afraid of adversity, some of us might be able to offer something from our life experience, but what you need is advice on relationships, and possibly when to end them. The forum members here have a lot of collective knowledge on cancer, but no more knowledge on relationships than anyone else in the world.
I have to say any internet forum on relationship breakdowns is not likely to be offering impartial healthy advice, there will be people with an axe to grind. Probably a counselling service like Relate might be a better place to go; almost certainly on your own at first, as it is unlikely your OH will engage.
So feel free to post if you want a sympathetic ear, but if you want to make progress with your life, get advice from an organisation that knows about relationships.