So, you had nerve sparing.
It might take up to 2 years to recover - you are 4+ months post op.
Have you seen any slight signs yet, such as lengthening, or even any feelings that something might be stirring when suitably aroused? Not to worry if you haven't yet, but those are the first signs of recovery.
You need to check with your consultant because of your multiple post op issues including urethrea and bladder stitches failing, but normally you can start penile rehabilitation by now. Having no erections for an extended period will cause the growth of fibrous tissue inside the penis which will impact erections when they do recover (reduction in size, hardness, and possibly curvature). Penile rehabilitation is generating erections artificially to preserve the function of the erectile tissue in the penis until natural erections return. There are several ways to do this, vacuum pump being a common one.
You should also ask for a daily low dose PDE5 inhibitor, which will improve blood flow inside the penis, and also serves to help maintain health of the erectile tissue in the absence of erections, and may help produce natural erections earlier.
For penile rehabilitation, ask your hospital for an appointment with an ED clinic. In some areas, there is no ED clinic and GP's carry out the function. However, these appointments can have a long waiting list and, providing your consultant gives you the OK to start, you shouldn't delay and might buy yourself a vacuum erection device. You can also look up Penile Rehabilitation on the web.
There's a longer posting on this:
https://community.prostatecanceruk.org/posts/t21301-Penis-size#post216227