I'm sorry to hear that you've had some problems following your prostatectomy. It's not an uncommon side effect and just a few days ago [@Cknchris] posted this thread about the problems that he's been experiencing. Hopefully as I've tagged him in this reply he may post to chat with you but you might also like to think about replying on his thread.
I wanted to let you know that Prostate Cancer UK runs a sexual support service and I wondered if this is something that might be helpful for you.
I hope that you're able to connect with others who have been through similar experiences and that you find the support you need to improve your relationship.
