Hello Di,
First, I know how terrifying it is to get that path report back and it is not what you had hoped.
10 years ago my husband received a very similar report, including perineural invasion.
I did a lot of research and bottom line, the presence of PNI means that the pathologist has seen prostate cancer cells surrounding or tracking along a nerve fiber within the prostate. It's presence on the biopsy signifies a high likelihood that the cancer has escaped the gland. We knew from the surgical summary that my husbands tumor was located in the Apex of the prostate which is the narrowest section of the prostate gland and shaped like a teardrop.
In our follow up with the doctor, we had so many questions. We knew that my husband's margins had been invaded, thus the presence of perineural invasion, and were VERY WORRIED about the "wait and watch" approach of our doctor in light of these findings. We were also concerned that because my husband's nerve bundles had been spared, there was a greater likelihood that cancer was left behind. Again...so many questions and concerns, much like you and your partner.
In the end, we wished we had chosen to follow through with our instincts to seek opinions from an oncologist. We did not and exactly two years later, my husband's cancer returned and he ended up having to have an aggressive round of salvage radiation treatments.
Our only suggestion is to honor your instincts., even if it includes a second opinion, and only then can you make a decision that feels comfortable for you both.
God Bless you and sending PRAYERS for a peaceful heart in the days ahead.

~Carla