I'm in a similar situation. You're not alone.

Therapy is a good start for sure!
Good on you for having clear boundaries and being firm about them -- realising that his current state does not live up to your expectations of a life partner. I wish I'd had the courage to leave with dignity like you.
Please take the following with a grain of salt. The problem in my relationship was that I attached to a False Self, the grandiose projection of/by my ex which he presented at the start (and which cropped up every now and again even later): loving, kind, affectionate, empathetic, protective, enthusiastic. Over the course of the relationship, I had to realise that this was but the highlight reel at best, if not complete fiction, and that his True Self didn't really exist. There was only angst, shame, guilt, a huge lack of self-esteem, fear of abandonment, enmeshment and co-dependency, all of which contributed to a toxic push-pull dynamic.
That said, even now that we're broken up and I realise I've been living a fantasy completely divorced from reality, I keep hoping for him to "change" and be the man he never truly was in the first place. The only way forward is to remind myself every. single. day that what I thought I loved was a mere spectre, a fancy, a folly. The mind knows this. The heart however has a hard time catching up. "But he
was special. He's so different from all the guys you've dated before/are dating now." That's the trickiest part to navigate.
It's a rocky road.