So.. Yeah.. My dad (59) is dying..

Just had to get this out there - more for myself than anything, really.
This is going to be a fairly long one..
I'm not an English speaking person, so my English might not be the best, but whomever reads this; I hope it's bearable at least - but again - this is mostly just for myself, as I just have to get my feelings out there, or else I'll just burst..

I wasn't raised with my dad around. I got in contact with him when I turned 18 (now 36), so I didn't really have a father figure around for the first 18 years of my life, but the next 18 has been amazing in that regard.
We did the usual father & son things. We went fishing - A LOT. Lakes, shore sides anywhere! It was amazing. More so the time spent together, than the actual fishing.
I know had a new best friend, and it was my dad! I was on the top of the world. Really.
I had missed a part of me/my life (or so it felt), growing up - but had since found it.

Now, my dad didn't have an easy time, when he was younger and around the time my mom and him got pregnant (sever pain issues, which caused a sever drinking problem) - which was what caused the separation to begin with. He's no saint, don't get me wrong. But at 18, I was willing to look past all that, and he really did seem to have changed, yet still kept drinking, albeit a fair bit less.

My dad has also always been a HEAVY smoker - we're talking 60-ish per day. This is what now ends his life..
A few years back, he got put on oxygen (he now waddles around with a backpack that has an small oxygen bottle in it, whenever he leaves the house for a little bit - a bigger one, if it's for a longer period of time). Smoking had absolutely killed his lungs. He got put on a waiting list for a "new pair", if he could prove he could stop smoking.

He fucking did it! He stopped smoking!
We were all so fucking proud of him! That was not an easy challenge for him - but it was either that, or slowly dying..

..and this is where it all changes..

About a year ago (maybe a bit longer), the doctors found 2 "spots" on his lungs. They weren't really worried at first, but they ran some tests and it turned out to be cancerous.
I've never cried as much in my life, as I did that day, hearing this.
Just writing it now, absolutely kills me.

He went through treatment, but was told, that he'd have to be cancer-free for 4 years before they could put him on the waiting list for a "new pair" of lungs.
He took the "challenge" and went all-in. He kept his mood up, the best he could and he ended up fucking BEATING CANCER!
Just a few months back, he was in remission!
Everything is going great! They even say, that with his current health, he might stand a chance at being fit and ready for a "new pair" of lungs in 4 years.
Fucking amazing!

...until yesterday.
My dad went for his regular check-up at the hospital, and they were absolutely amazed he even showed up, as he was already declared "Terminal" (they didn't tell him this, so straight forward, but that was the just of it) and didn't need to go to these check-ups anymore, which he wasn't informed about - so that came as a massive shock.
He got pulled into a room and a doctor came to talk to him.
My dad called me, after getting home from the hospital.
He's got 6 months (give or take) to live.
I didn't even know how to respond to that. We knew it was going in that direction, if things got worse with his lungs, before he could get put on the waiting list - but we NEVER expected it to happen now - and not like this..

He's been planning his birthday (60), which is just a few months away - but now he's not even sure he's going to make it to that date.
He is absolutely destroyed. As are we all. He fought so hard, and now it all feels like it was "for nothing".

I'm having a real hard time just writing this. I've never felt so defeated/destroyed in my life.
This sounds so freaking selfish, but I'm losing my best friend - my dad!
It feels like I've only just gotten in contact with him again, and now he's only got 6 months left to live..
I'm absolutely crushed/destroyed. I don't know how to feel around him. I don't know how to feel around my wife. She knows this is hard for me - she's having a hard time with it as well.
But.. Yeah.. This is.. Well.. It just.. is...

Thanks for reading this, whomever stuck it out through my sob-story.
As said, this had been more for me, than for anyone else. Something to "throw out there" - scream/cry into the void - let it take some of my sadness, because I'm fucking overflowing with it right now.

Edit:
Thank you all, for your kind replies, suggestions and sharing of your own stories.
I will for sure take them to heart.
It warms my heart immensely and has eased up my feeling a bit, this morning, more than I thought it would.
Thank you all, from the bottom of my heart!