It's not clear to me quite what his and your collective situations are. He may have tried to masturbate and found he couldn't get an erection (indeed, that's highly likely shortly after the procedure). He may have a sense of failure and dread at even trying that again, never mind sex with a partner. To prevent getting into that situation, he may have put up a barrier to being intimate in any way. (A lot of "may"s and guesswork here - I could be on completely the wrong path.)
I think there are a couple of things to try here.
Try to restore the intimacy, but with the pressure to have sex removed from the equation for now. You could do this in a couple of ways. Depending how well the two of you are communicating, you could discuss it as a plan, and agree sex is off the table for a month or two, but you want to get back to kisses, cuddles, stroking each others shoulders, arms, hands, etc, whatever you might have done in the past, except sex. Even if you both find such a session starts heading towards sex, don't go there - you need to get your intimate bond back fully working, and not at this stage try anything which might fail and knock it back. If that level of communication isn't operating, you could start by trying intimacy in circumstances where sex can't happen, such as in public, walking hand in hand, arms around each others' shoulders, having a good snog, etc. This might help you improve communication, but you'll need to work on that too.
This brings me to a communications activity I suggest for couples to try and help communicate again when communications have been damaged by distancing caused by loss of sex. Each of you go off separately with a sheet of paper and think of the following things to write down:
Think of a question to ask about how prostate cancer has affected your partner.
Write down an activity the two of you do which is important to you staying physically close.
Write down an activity you would like to do to make you physically close.
When you've both done this separately, come together, and discuss your answers one by one.
You can repeat this again in a week or two (decide and put a date in your diaries so it doesn't get missed), and you have to come up with 3 different points next time.
If you can get intimacy (without sex) going again, and communications going again, you should be able to come together and both understand each others' issues, and start formulating a plan. If you've wanted to continue on to sex during your month or two of intimacy with abstention, you should now be in a position to discuss if it's time to give it a go, or to understand why it isn't going to work (e.g. ED), and talk about what you might do about it. There are ways to have sex without an erection, and there are ways to get an erection with assistance, but you won't be able to talk about these or have the confidence to try and risk failure until you are back fully communicating freely again. You need to handle failure sensitively, as far as possible by maintaining intimacy, such that any failed sex isn't seen as intimacy ending in failure, but the intimacy continues.
Wishing you the best of luck.