He's off to pastures new, and being unkind to you in the meantime - you who have supported him through his mental health issues. Sadly, I've experienced this before - when the unwell person gets better, they have new-found confidence, and off they go. It's scary, this is a different person mentally now, but he's made his decision and you did exactly the right thing.
Are you going to be OK on your own? You need to grit your teeth and stop letting him make you think this is your fault - it's not, it's a man on a mission.
We're here if you need us - please don't go through this on your own.