I’m sorry iccarus. I don’t know the whole story and know these things can be complicated and cause a lot of stress and burden and deep emotions. My words feel weak as there isn’t really anything I can do to help you through, but they are sincere and you have people hoping the best for you and here to listen, for what at least hopefully at least small comfort that might offer.

I'm so sorry for your loss. Sending you virtual love and comfort - you are not alone xoxo

it's just the family luck, i've been visiting every weekend to see my dad and help out. Last weekend, my bike broke down on the freeway on Easter Sunday, so no bike, no way to visit, sure i can go next weekend. But the one weekend I can't make it, is the last time I could have seen him.

I can’t imagine how you feel. I know that not knowing the last time you speak to someone is the last time- that can deny us feelings of closure or make us wish we had said or done things differently. I just hope that last interaction you had was pleasant- or at least genuine. That there is some solace to that.
It can’t erase loss or change what happened- but if you at least had a positive last interaction or were able to express yourself naturally- even if you feel like you didn’t get your proper goodbye or had things left or say- at least having that last chance you didn’t know was your last- and having it be something other than negative- that’s more than we are promised in parting with people. I’m sorry things went the way they did- I just hope you can process it in your way and your time, that you can find some comfort where it may be found in between.

last interaction was just after he woke up:
Dad: oh, you're going home now?
Me: Yeah, going to rain a lot tomorrow, so best go today
Dad: Ok, thanks for coming
Me: bye dad
Dad: Ok

It’s not my place to tell you how to feel about that, but for me personally, even if I didn’t know that goodbye was my last goodbye, it would be a goodbye. As normal as a quick exchange about the weather may seem- it’s kind of all there- your dad being thankful for your presence, you saying goodbye. The sort of mundane nature of it- how it’s such a natural and not forced kind of interaction.
It’s up to you to interpret it for your own self of course- but I see some poetry to this as a goodbye, and while subtle an obvious care between both of you for the other.

he wasn't much for talking, we never had any father son talks, or anything meaningful, but he's still my dad

Still is and always will be. From the conversation you mentioned- I got the feeling he wasn’t the biggest talker, his personality came through a bit I felt, and I think maybe that conversation was very “him” and very “the two of you” and a moment between you both that has more depth than one might glance. What I mean is that people who don’t talk much tend to say alot behind their words. My father was never a big talker himself, he sort of figured that if you were close to him, you knew what he felt without the need to say it so obviously- and generally I felt like I did even if sometimes I had to think on it a bit to really understand what he was meaning or feeling. Maybe your dad is similar, or maybe not. I hope you are able to take those happy moments no matter how small and hold on to them. Chances are if you knew how he felt he knew how you felt too. We never have enough time, but I hope the time you had was good time.