Keith: “I said I wouldn’t cry!”
So does this mean Keith cries whenever he’s faced with something personal? This implies that he cries regularly for some reason (or used to), though that reason is still speculation. But seeing how he has a temper (and realizes that), I’m betting that dealing with personal issues does, in fact, make Keith very upset, which is probably why he doesn’t do it. Some people in fandom think Keith isn’t very emotional, or has very strict control over his emotions, but I’ve always thought it was the opposite. I think Keith just removes himself from potentially emotional situations when he can so as to prevent himself showing emotion or getting upset (like how he never said a single word to Allura after she found out he was Galra. He just stayed quiet while she was angry and even after she later approached him, he didn’t say much because that, too, would likely have made him upset). Anger is harder to reel in on the spot, so him losing his temper is more expected, but I’m betting Keith knows that horrible, suffocating feeling that wells up through you when you’re upset and can’t stop the tears. And so he avoids it whenever possible, thus resulting in him avoiding talking about his personal issues.
Unlike Lance, who is often portrayed in fanon as the emotional one, but that I think has considerable emotional control. Lance very rarely gets upset or loses his temper, despite his insecurities and how much he misses his family. He jokes around and whines, sure, but that’s a conscious kind of display that he uses, I think, as a defense mechanism. The only time in the show that I think Lance has gotten honestly angry (and I don’t mean simply annoyed like when the black lion rejected him (although I think that did upset him to a certain extent) or desperate like when he was trying to pull Keith back in season 3) is when Shiro chose Keith over him to go into the Marmora Base. Lance gives off an aura of emotionalism as a way of hiding how he really feels, and even when he does get angry, he pulls back quite quickly and doesn’t usually end up yelling, like Keith does.
Just some character thoughts I guess.