unable to get an erection and keep

After having the snip about 20 years ago, i could still produce semen.  Since having diagnosed with PC and had all the treatment with 2 years of prostap injections, i have become unable to get an erection to be able to penetrate, I do not produce semen anymore so having dry orgasms. I have been off the prostap now for 2 years and my PSA has gone up from 0.01 to 0.04 which isnt a big deal, but i am getting frustrated in not being able to get and keep an erection and even more so not being able to produce semen. Is there anything else other than Tadalifil which i am taking on a daily basis as i have been attempting to make love, but this is now a no-go and my partner has left me.