Unfortunately we are no longer together, but my partner and I used to fly together a lot. I would say that there is a big difference between flying with a fellow pilot and flying with someone you know intimately (
intimately as in the way they think and are likely to react to situations).
Where something may need to be clarified with words when flying with a fellow pilot, there were many occasions where a glance would tell me exactly what she was thinking and vice versa. This is particularly helpful when the P1 is under pressure, as a deeper understanding of each other, enables swifter solutions.
Even when flying under no pressure, I didn't have to ask for something, she always had it ready. She was very good at navigating and would for example, automatically have frequencies ready for me at the right time, just as I was about to ask for them. Plus a multitude of other examples, but at the end of the day it made flying so much more pleasurable when we knew what the other was thinking. More time to look out the window and revel in the view.