No @Sabze it won't be easy. I had to tell my niece and nephew (8 and 11 at the time) that I had the same disease that had killed their mother 17 months earlier. My husband and I are raising them with my older two kids. It was the single worst thing I've ever had to do in my life. Hands down the hardest. It still turns my stomach when I think about it now. But there's nothing for it. You just have to take a deep breath and do it. Like taking off a bandaid. My husband did it with me.
My father-in-law also lives with us because 10 months before my sister died his daughter passed away from a glioblastoma. It's been difficult all the way through, and still difficult now to give rein to my emotions. He is such a wonderful, stoic, cheerful man who's had a lot of tragedy in his life (his wife died at 39 from an aneurysm). I never want to upset him with my distress. So I think I understand the stress of the consideration you're giving your partner.
That's where this forum is incredibly useful. Unload here. There's always someone who gets it. K xox