Erectile Dysfunction (ED)

I had prostatectomy surgery 16 months ago. I haven't had sex or even an erection since. I had everthing removed in the surgery and no nerve saving. I don't understand why the prescribed me cialis when I don't have any nerves for them to effect. I even asked the Doctor. My relation with my Wife is great due to there being other way I can please her. I still feel guilty about not being able to get an erection. I purchase the pump and get an erection but as soon as I remove my penis from the pump it goes limp. It's even hard for me to share this with you all but maybe someone in the community might had their nevers and all removed. Thanks,