Loss of semen can be a big issue for some men. When I was being treated at Mount Vernon, it was one of the questions they asked all patients, if the loss was a significant problem for them, and I believe they provided counseling to those wanting help with their feelings in this area. You might ask if something similar is available from your hospital. Don't think that you're alone, or that it's insignificant - this is a recognised issue.
I've also worked with some men who have climaturea (peeing on ejaculation). For some, it's a significant problem, while for others it's a good substitute for missing semen. Everyone is different, and what upsets one person may be quite satisfying to another. You shouldn't feel bad whichever applies to you.
So you might consider asking for some sexual counseling, which you should be entitled to via your GP as a prostate cancer patient. They may be able to show you ways to enjoy your changed sexual function.