The only reason I’d even consider giving a second chance would be if he’d he’d recognised that his behaviour was abusive, started making changes immediately, then also chosen to go to therapy/anger management because he’d made an independent decision to get help with this - and he’d done all of this immediately after the very first time you’d ever spoken to him about it, before things escalated. Even then I’d be wary about his motivations.
As it is, he’s only promising to change because you left. If he can choose to change now, he could have chosen to change at any point. So why, when you were repeatedly asking him to stop and explaining why, didn’t he choose to change then?
All of his behaviours were choices, and ‘mental health issues’ are nothing more than a predictable excuse designed to make you feel guilty if you don’t forgive him. If he hasn’t been shouting at his friends or his boss, hasn’t been throwing things or slamming doors around other people, if he’s not in the habit of stopping anyone else from leaving rooms when he’s angry, he has - and has always had - control over his actions.
He says he respects me and sees how bad it looks and how he’s scared me and it’s taught him a lesson
Is he really so stupid that he needed you to leave before he could learn this lesson - your repeated explanations weren’t enough for him? And, despite this, he still hasn’t acknowledged his actions were abusive?
It “looks” bad because it is bad. If he didn’t want to look like an abusive prick he shouldn’t have engaged in abusive behaviours, should he?
A lot of the advice around recognising abuse talks about early signs appearing within months. I’ve seen very little talking about men who manage to keep the mask on for years…but they do exist. If you gave him another chance he might manage to be on his best behaviour for a while, but you’re probably right that he’d “just get better at being angry in less obvious ways”.
You’ve already done the hard part and left him - so don’t doubt yourself now. Ignore the unhelpful opinions of your support network and listen to what your gut is telling you.