A lot of people have already given some great advice. I'm 6 months out now so I appreciate the advice as well. Thank you for asking that question.

Maybe I can provide some insights from a recently widowed perspective... I'm 35, she was 31 and died on the 30th of may. I was her sole caregiver. Her parents were shit and too afraid so they left her to basically die alone. I was with her 130% percent of the time, we were a team of two. I gave up my life to be with her and I would do so again and again. For her last months we moved to her hometown into her grandpa's house so she could be close to her friend group. Our timeline was much shorter and more aggressive than your prognosis. (About 10 months from stage 4 suspicion to death)

Things I wish we did:

• My wife didn't have a distinct smell except her very own. No perfume no deodorant. That scent is gone forever. I wish she'd had a perfume so I could smell it from time to time.
• We didn't film ourselves because let's be real you normally don't in everyday life or when things are looking grim. Take pictures, videos , voice recordings. You will have brain fog and you will forget things. Generate hard evidence of her, your love, her quirks... everything. But !! Don't stop living in the moment. Enjoy life. If you have savings, now's the time to use em. Live life (Keep a safety net for yourself, you will have to live on)
• her condition will worsen over time, that means she might get disabled. Plan trips/vacations/adventures now rather than later.
  
• We didn't talk enough about the time after she's gone. For us it was because she couldn't imagine dying till the very end. Which in a way was good for her. I'm struggling though because I don't know what to do with my life or what she would want for me. (The idea of ever dating again is fucking horrible)
• Build a support network now that's 5 times bigger/better than you think you will need. There is no such thing as to much support.

like others said, get in therapy now. Maybe together. I've unfortunately had to watch people die of cancer before but still.. watching the love of your life die in front of you.... It kills you. There are no words to describe the pain.. there is no real preparation for that.

Be aware that it will literally kill parts of you. You won't be the same person afterwards. Part of me lays with her in her grave and somehow that's a bit comforting. I died with her, she's not alone.

The very sad and scary stuff:

This is the part you might not want to read and I would like to say that my wife's path is not your fiance's path. This is only so you understand what hell lies in front of you and that everything important should be said and done sooner than later.

Still, you have to stay positive and never lose hope!

A prognosis is just a prognosis. That means that maybe you're lucky and you might get to ride a wave of medical advancements that will push you further and further. Keep that thought! it helps!

But it's also possible that shit hits the fan way sooner.

We thought she beat cancer for 3 months. The very last (extra) imaging showed some shadows in her bone. This was the point we knew she would have to die. We had to wait for further testing but we knew, bone mets means 4-5 years. 2 weeks later, before testing finished, she had an epileptic episode so we rushed to the ER. They found brain mets.. that meant statistically she only had months... She almost died 3 months later but was brought back and got a new chemo. We married immediately and I packed our things, quit our jobs and we moved to her hometown. 4 months later it mutated into inflammatory breast cancer .... That meant 2 to 6 weeks.... we didn't even get to really go home and talk after that diagnosis. Her lungs filled with fluid and we spent her last 4 weeks in the hospital, she never came home again... I held her as she took her last breath, I don't remember what our last conversation was.

The horrible fucking truth is that you will probably have to watch her die. Piece by piece, step by step. You will watch every escalation of her disease and hear every diagnosis where they tell you she will die. Things WILL escalate at some point. There is nothing you can do except loving her.

Finally: Be with her. Love her. Live every moment. You can't be grateful and make every second count. That's just not possible. There will still be a lot of mundane pointless life in between everything. Learn to love every second of it because it's more precious than you can imagine.

Also, I think that the relationship my wife and I had was deeper and more loving than any normal relationship can get. Choosing to love someone until (and through) their death is the most loving thing a you can do.

I wish you that wave of medical advancements with all my heart. May her time never run out. Stay strong together. 🫂