Advice on writing platonic love between best friends?

so basically, for a novel I'm working on, there are two best friends who meet when they are both about freshman (14-15) in highschool, because they become neighbours.
They quickly become friends and bond and then best friends. The two then continue into early adulthood as best friends, until one of them dies…

I know the basics for writing a best friend relationship, but I want to be able to show that it is purely platonic, yes they love each other, but it is in now way a romantic attraction, more like a personality one… I dunno if that makes sense?

I want to be able to show that these two characters are very close in terms of relationship with there being no romantic aspect.
I want to be able to show this by more than just making them not kiss and what not.

I will take any advice because I want to be able to make this relationship very detailed and in depth, because I need to be able to do that in order to understand the grief the character is going through, once the other character dies.

I have a relationship like that with my best friend, and I think one of the closest ways to describe that type of platonic love is that you see the other as family, but with a deeper bond. Like, in a family, you can be yourself for the most part but there are some things that might not be acceptable (like cursing in front of your parents or younger siblings, brining up certain topics, etc.) However with your best friend, you can do all of that and you'll never be judged or criticized for what you think, no matter how stupid or outrageous your opinions might be. This person is like the other half of you that you feel incomplete without. They're the one that seems to always know when you're having a bad day and they'll do what they can to make you feel better, whether that's trying to cheer you up or give you space, but they just always seem to know, to understand.
I'm sorry for going on a tangent, but basically that type of friendship would be best described as them seeing and loving the other as family, except that they're the family member who understands and trulu accepts every single part about you, if that makes sense

it does!
Kinda depressed that I don't have that kind of relationship with anyone now—
but thank you!

No problem!