Curate, connect, and discover
It's here. The "Keith gains two new friends in one fell swoop" chapter. I was going to call it the "Keith acquires more than one friend" chapter, but I think at this point he would call Hunk a friend. Hunk is actually...probably the person Keith's age that he would call a friend.
So, to be clear about their relationship, if you were to ask Keith at this point what he thought of the boys (Shiro, Adam, and Matt) he would tell you that they're his friends and would probably call Shiro his best friend. This is true, but there's also a little more to it.
I like the idea that the Galra were originally a pack species. A lot of time has passed and evolution has occurred that makes it less obvious and Galra don't necessarily feel to drive to create a pack or bond as such, but they are comfortable with it and it satisfies a part of their natural instincts. Similar to how humans are a social species, but not necessarily every human needs a lot of socializing and many of us can choose when to socialize and for how long to satisfy ourselves, but in the end socializing and creating bonds is satisfying for most of us.
So, Keith, being half Galra, has some of those instincts. He isn't actively seeking out a "pack", but Shiro, Adam, and Matt are slowly integrating themselves into his life in a way where he would instinctually consider them to be part of his pack, especially since they're younger than him and he feels a responsibility towards them as a teacher. It's satisfying for him and so he's getting something out of it that simply socializing with other people has never given him before. Having a give and take at the beginning of a relationship helps center him around people who he considers to be strangers; which is why the start of his relationship with Shiro was so rocky. He wasn't sure how to interact when it was just Shiro talking with him, but once he had something to contribute (teaching Shiro to fly) he felt more comfortable around him long enough for them to establish a greater bond.
Anyway, this chapter is from Matt's perspective and I'm running my mouth on Keith headcannons lol. Matt's just a silly little guy. He's the youngest and he has simple needs and wants and does not allow anything to get in his way. Which, you know what, good for him
Enjoy the chapter while I untangle the MESS that chapter 13 has turned into