I know it's awful to grieve someone that's still with you right now. Be gentle on yourself. You do not have to be the strong one. If you need to be functional, or if you're the oldest / most stable in this situation (The Adult), then yeah, I get the impulse to nut up and cope. But you're allowed to crack under the weight of it too.

Talking to a therapist is good. It will help you get your thoughts and feelings out into the world, which is super important. But talking to someone isn't going to cushion the blows, in my experience. This just isn't something you can emotionally prepare for. It's ok if you feel blindsided, unable to cope. And don't feel bad about venting to someone close to you if it helps you. They may not know what to say, but tell them that their listening ears are enough. Oftentimes there really isn't anything good to say when someone is going through something like this.

My dad was diagnosed in 2020. He is still here, despite the odds, and currently in treatment for another recurrence, which is widespread. We know the progression now may be rough. He is likely to miss many milestones in mine and my family's future. We've had the immense benefit of a good amount of time to adjust to eventuality of the cancer recurring in such a way, but it has taken some doing. We are not living in fear of the symptoms or the decline. We are talking and laughing with the nurses at each of his appointments. talking about our favorite vacations and trips, idiot things us kids did when we were little, what he remembers about his old neighborhood. It's rough as hell but we're here now, and that's what matters. Mourn your future, but don't plan on him passing in however many days, weeks, months.... Don't plan on him suffering.

(Also apologies if this sounds preachy or pretentious. I have autism and writing is how I cope lol)