1) Personally, I think a good relationship needs understanding: You have to either build it, or show that it's there.
You want the people involved to know things about each other, to have a history with each other. Go beyond just smooshing their basic personalities together and seeing what happens; have them share experiences that they can look back on later.
I mean, that's kinda the difference between a 'friend' and a 'best friend', right? A 'friend' is just someone you like, someone you vibe with and talk to sometimes. A 'best friend' is someone you enjoy spending time with, someone who understands your wants and needs and can support you.
2) An emotional death, huh...I think there are two main things you need for that:
-A sense of unfairness
'Time' is just giving the audience/characters a chance to get into their emotions. Give the dying character some final words before they croak, or if they die suddenly, give the surviving characters an emotional reaction (or do some fancy cinematography so the audience has time for their own emotional reaction).
I mean, just imagine if you did neither: The character is randomly shot in the head, dying instantly, and just like that we're onto the next scene as if nothing happened. It's borderline disrespectful and almost confusing...definitely not what you want if you're looking for pathos.
'A sense of unfairness' is just...exactly what I wrote. You want the audience especially to think "NO, NOT YET!" "IT'S TOO SOON!" "THEY WERE THIS CLOSE!"
Honestly, unfairness hurts even more than loss...or rather, it's one of the main reasons why loss hurts so much. It's watching the universe give a giant middle finger to our hopes and dreams and not being able to do a damn thing about it. ^^;
You should have a sort of base level of unfairness if the dying character is likable enough...people will not want them dead simply because it means they won't get to see them in the story anymore.
The next step is upping that level with circumstances~. The character dies...minutes after they finally make it home from the war. Or minutes before they finally make it home from the war. ;]
The character dies...just as they were starting to turn their life around. The character dies...just as they were starting to trust the protagonist. The character dies...just as they were beginning to have hope that things could be better for them.
Of course, be careful not to make it look like you were 'stringing people along' just by building up to a character death (this is apparently a big issue with LGBTQ+ relationships in particular). It's one thing for a character to have a heartbreaking death in a war story, where characters are dying left and right anyway.
If your story will only have a few special deaths, you have to take care not to make them look like "punishments", or easy escapes so that you won't have to deal with writing what comes after a big moment in a character's life.
Like, if two characters finally get married and immediately afterwards one of them dies, did you do it because their death means something to the story, or did you do it because mature relationships are boring to you and you don't want to write a marriage? Fans are surprisingly good at detecting stuff like that, and if a death feels unfair enough to them they will look for bad intentions (even if there are none). Watch your back...