So this isn't based any one character that I'm creating yet per se, but just a rando thought that popped into my head. Hypothetically, suppose a character whose already proven that they are brave and often act before they think, gets themselves into a situation, where their actions get's their loved one killed. Which means: angst, angst, angst. But what is the best way for said character to overcome that? Obviously personal growth for them is required to be a better person
I think it depends. Some people change very easily. Some people do not change at all. So I think you should ask yourself: What would make this guy change what he's doing? Why is he doing what he's doing? Is he charging in headfirst because he's a dwarf, and he has deep-rooted cultural beliefs about dying valiantly in battle? Then he's probably not going to change what he's doing unless he decides that his friends' lives are more important than his cultural traditions. Is he charging in headfirst because he's young and naive and thinks this is how people win fights? Then he'll probably stop if he's given evidence it doesn't work. Does your character respond to being given evidence, or does he get angry and lash out and insist his friends got THEMSELVES killed? Is he kind of person who gets defensive, or is he the kind of person always striving to improve? Is he low-emotion or high-emotion? Does he get angry at future friends and insist they stay behind where it's safe so they can't get killed, then continue charging in head-first himself? I think it's up to the writer to decide how their character changes.
If the character is motivated by their emotions, they might think they are doing the right thing. Then when they fail get someone near and dear killed, they realized that they need to rethink their motives/actions. Like charging into battle to save someone, then realize they are running into a trap that gets innocent lives killed. Guilt weighs heavy on them, but personal growth allows them to mature, and be better for it. Like Costner from Robin Hood when Sherwood gets attack.