I ride with a partner often. We do and havve done some huge trips at short notice and for us it works most of the time and I do have a great ride mate.
The thing is we did hundreds of miles and plenty o f trips in the lead up to our first big one. We had clicked.
Now the thing is Pressure to perform and not "wanting to let the side down" can be a negative problem.
If you go the solo thing then If you need to stop then you stop. Two of you has a new dimension. Think it though and dooooooo pleeeenty of miles together to settle in before the big two show trip.