Hey, I know how you feel. At the six week post surgery point and with no semblance of an erection using Viagra I too became depressed and wondered it I chose the wrong treatment. I had considered proton beam because of the half dozen or so guys I had contacted that chose that treatment and they had very little side effects and all were fully potent. I chose Da Vinci for the piece of mind.
As recommended by several who have responded try the pump. It allowed me to be able to have intercourse but lacked in quality. It is very good for rehab. I eventually moved to injections. I am using Bimix due to pain with Caverjet. The Bimix gives me an erection that is very firm and almost like the ones before surgery. I just had an appoitment with my urologist on Monday for my six month post op check. We discussed the ED and he recommended that I combine the Viagra with injections to further stimulate the penis. He told me that it can take up to two years after surgery to get normal erections back.
The best way to get passed the depression is to take action so I would try the pump or talk to your urologist about injections. As my urologist told me men that are highly motivated generally will go straight to the injections. Those that are not will go the pump first. You have to try the pump to know whether or not it is for you. It was not in my case.
Note that you are still healing.