1. Clear that Gus knew. Nacho didn't rush in to help Hector, he focuses on picking up the tablets and medication. Showed no signs of fear, emotion, nothing.
Where it gets really interesting is this: Does Gus 'appreciate' what Nacho did? Or, will Gus find it disrespectful? It would not surprise me if it is the latter.
2. I am torn on this. I think 99% of what Chuck said was real. The truth, his truth. And in some ways, he is 'right'. Jimmy is a danger to others, or at least some of his personas are. Jimmy was right also, Chuck was not innocent in all this. And while Chuck didn't acknowledge it directly, I think he did inside.
The final comments 'you never meant anything to me anyway' was heartbreaking for Jimmy. He walked away, the classic 'should' I turn around and go back'. He chose not to.
And just as Jimmy went out of sight Chuck looked up. I think, because he knows both are in the right and in the wrong. And a part of him deep inside did and still does care for his brother.
3. So why? The answer is, we will never know. Or likely never know. We can speculate atleast.
His journal/diary, when he woke up in the middle of the night, had a series of feelings at different times of the day. As he wrote something in, he did not write a feeling. He felt nothing.
So why end it all? If I really simplify it, there are two scenarios running through my head.
a) What have I got to live for? Chuck lost. He thought he beat his condition, it came back. He thought he could win back HHM, he didn't. He thought he could help his brother, he couldn't.
So what is there for Chuck to live for? Nothing in his eyes. It has all gone. Time to end it all.
b) Do I deserve to live? Chuck realised, deep down, what he had done. His condition, which is a genuine mental illness remember, caused so much harm to him, his career, his loved ones.
In some ways a parallel with what he accused Jimmy of. His condition brought sadness and harm to all around, including himself. Maybe his final words to Jimmy were resonated with him?