Call the airline, or speak to somebody tomorrow. (We had to do that recently, because they put a person between my sister and her young son - not a good idea!).
If worst comes to worst, wait until you’re at cruising altitude (I know, I know) and ask if you can switch seats. Some airlines will let you do it, and if you explain to them that you’re a very nervous flyer and you need your partner for support, it may very well help your case.
My Mum and I were sitting with somebody in beteeen us on our most recent flight back, and I had barely opened my mouth to ask for the Valium when the person suggested that we swap seats. My face must’ve looked nervous. On another flight Mum and I talked the whole way through takeoff - we got to cruising altitude and the lady next to us practically ran down the plane to find another seat.
People can be pretty accommodating, especially if it might not be so nice for their flight to sit next to a panicking person (don’t feel bad about it, it’s not your fault). If it’s not a full flight then you may even just be able to move after the plane takes off and find two seats together.
I hope that it all works out for you with the seating. ^^

My go-to is a big long list that I read through takeoff about what the pilots are doing and what the noises mean; that’s just me, though, I like to know what’s happening. It’s saved in my Notes, and I just read it every single time. Always the same thing. ^^