@rycliff_24Among the ways for a person or character to have a significant (moral) change are:
Near Death Experience many people make a significant reassessment of themselves after such an experience. Serious consideration of is there a God, an "afterlife" or just how will people think of me when I am dead. This could be a mistaken diagnosis of cancer, or brakes failing on a steep and winding road, nearly drowning, or while engaged in a nefarious activity a crony gets his brains blown out, then the gun is pointed at the character. Or even being shot and expecting to die... only to wake up in the hospital, or even on the ground.
Kernal was already there earlier in the story it was established that the character had a moral compass; a particular firm grounding, such as "Never Hit a Woman." When they face a "Moral Event Horizon" they refuse to cross That line. Resulting in a re-assessment of what they have been doing for some time.
Road to Damascus moment Not necessarily a "Thunderbolt from God!" perhaps the character always wanted to be Respected, suddenly he notices he only inspire fear, not respect.
I have not yet read your story, but intend to. Let me ask, "He is the MC's best friend. ...does He view the MC as his best friend? If faced with Losing the respect and friendship of his Best Friend, would he change his ways, or remain willfully irredeemable?