I've name changed for this as some of my previous posts may be identifying and this is quite private.
My DP previously had testicular cancer and had one testicle removed. Recently, when we have sex I've noticed a decrease in the amount of semen he produces. It's not every time, but I have asked him if he has climaxed a few times as it doesn't feel as though he has based on the "evidence". I've discussed with him that I've noticed this change and he is, understandably, anxious about it. Although he hasn't noticed a change himself when he masturbates (we don't live together).
He had cancer prior to us being together, so this change has happened a long time subsequent to his treatment so I don't think it's directly related to that. But obviously he is concerned that this could be a sign that something is wrong with the remaining testicle, although he has no other symptoms.
Is this something to be concerned about? Or is there possibly a simple reason this could be happening? Any advice is much appreciated.