You are too emotionally involved in this to be objective in my opinion. You need someone that is very liberally aligned to asses the situation and take action accordingly. This is what I tell fellow mods. If a mod is participating in a thread, they are no longer a mod and should not take actions against others. Ask another mod to take a look and take actions.

Everyone has a right to have a bad day, and a right to be wrong. No one has a right to continuously bring others down. I would send the guy messages addressing this and see how he responds regardless of my biases and preconceptions. I would then notify him of my expectations for constraint. If he violates that, I would warn him, likely twice. If it happens thrice in a span of half a year, I would not hesitate to ban him. My policy is “first do no harm” and “live and let live,” but these apply to individual and group at the same time. Never be an authoritarian. All admin and mod actions cause harm that should be tempered with kindness empathy and reason wherever possible. Social interaction is an addition. Causing sudden withdraw in an individual may cause real and irreversible harm.