It’s been over a year since my best friend’s ex was killed, it still bothers me.?

My best friend was dated & lived with this guy from March to the beginning of June of 2016 (not knowing him long before they got together), not trying to speak ill of the dead but he wasn't such a good guy. He was in a gang, he was a drug dealer, a gambler, a borderline deadbeat dad, he was a setup guy/robber, he went to jail for aggravated robbery, baby mama drama, he was a opportunist etc. He only dated her for sex, money & free rides. One day, I was fed up with him taking advantage of her. I confronted him and gave him my two cent. Afterwards,I confronted her for being so stupid for this guy. A week later, he called me from her phone. He was talking trash & threaten my life, also my family's life. We didn't speak for almost a month & the day before he died she told I was right about him and she apologized to me, telling me she loves me. We patched things up and she was ready to move on from him, but the next day she told me the guy was shot & killed. He died because a week before his death, him and some of his friends set up someone too get robbed & shot, so his death was in retaliation. She was devastated & I felt bad because I love her, seeing her messed up over a guy like this was heartbreaking. I felt bad for not ending the bad blood while he was alive & it still bothers me to this day. I didn't like this guy but he didn't deserve to get killed.