My heart breaks reading this. You sound like such a caring man, trying to be strong for your partner. 
I would suggest showing her this, how much you love her, care and worry about her. 

I was in a similar situation with my mum. Stage 4 lung cancer. All I can say, is be there for her, exactly as you are now. Take time, to make as many memories as you can.

The diagnosis of 'nothing more we can do'. Is frightening, your future you had planned, all wiped away. Instead you're left with the unknown and have no idea, what is coming up. The questions: How do you act, can I cope, will I let them down. All perfectly normal, yes they are the main priority but you matter too. You want to be strong but your heart is breaking. You worry about letting them down, talk to her. Find out what she wants, tell her you're scared and want to do everything you can. To help her cope and do it together. 
I've just been diagnosed with cancer myself, same age as my mum was. I'm doing exactly what you are, ignore it and acting as normal as I can. We're making memories and making time, to do stuff we used to be too tired or busy for. Life is so precious and so fragile. Simply find out what she  wants and cherish that time together. Sending strength and hugs 

It's easy to be sat here saying you should be doing this or should not be doing that, but until someone has walked in your shoes, any advice kinda rings hollow.

You're dealing with things how i have dealt with things during my wife's diagnosis, so i can relate to you in that sense. I had many a late night thinking session, then kinda blocked it all out the next morning. If you overthink this sort of stuff, it will become all consuming, and that doesn't do yourself or your wife any favours.

You hear all this inspirational stuff from survivors or those dealing with a terminal diagnosis, and can easily beat yourself up because you're just not seeing or feeling what those people are. I've learned one thing since we began our journey, each journey is individual. What works for some, doesn't always work for others. People are also individual when it comes to emotions and how they process those emotions. You see it on here 101 times over. Some people are mentally broken by their diagnosis, whilst others take a positive approach.

You're needing time to process your situation, so don't beat yourself up. No one asked for the hand we were dealt, so no one is to blame.

What i would suggest, you have the option to call Maggies or Macmillan (or even both) and they can help you process your situation. They really are fantastic and are there for you too. Don't just sit there and suffer. you're going through this too.

Something i have noticed on forum is that lots of times family and friends can take diagnosis worse then the person with cancer. 

Hope things go well for everyone. 

Try to keep positive i know it harder than people think. 

Billy 

Thank you very much for you kind an encouraging words. There really is no handbook on how to deal with this situation. I'm very sorry to hear you are now diagnosed I do hope that you get through it cancer free in the easiest way possible. It's scary how common cancer diagnosis are these day and what even more worrying is how bad the NHS are at timely diagnosis. It's really made me think that getting private health for myself and my son might be the right move forward. All the best in your recovery!

Thank you for this it means a lot cause one of the biggest things I'm struggling with at the moment is the guilt. Guilt that we are not climbing mountains and touring the world but as we all know this is very much subject to finances and life styles and with having a little boy we can't just go and do as we like. But this doesn't stop me from feeling guilt. If I could do anything to change the outcome for my partner I would hell I would rather it be me that her. I guess I get the guilt from people around us expecting us to react in certain ways but at the end of the day we are still the same people in the same relationship. We still have squabbles and don't always see eye to eye but god knows I love her and would do anything to change the outcome. 

Thanks for you kind and encouraging words. I guess it helps to know that all of us are not alone in the fates we have been dealt. I mean I wish this hadn't happen to any of our families but at the same time it's nice to know we are not alone.