As for your (now former) manager, they showed their true colours when they said you lacked courage. Should have been more supportive.
A manager saying you lack courage is despicable and reinforces the idea that it was an unhealthy situation.
What is or is not courageous for you is for only you and anyone you invite to advise you on life choices. It's quite likely (but for you to decide) that your decision to quit was, in fact, the more courageous choice.
Your manager was laying on a guilt trip.
I too have worked for two small technology companies. The first one was great. Smart boss, heavy but realistic workload. Got bought out by a much larger competitor. Sales people making unrealistic commitments to clients, then project managers driving the tech team to breaking point with unattainable deadlines and budgets. It became toxic. Got bought out by an even bigger competitor, a multinational company. I refused to sign on to the third company. They had a reputation. If the second company hadn't been bought out I would have probably quit anyway.
Don't lose sleep over the manager's opinion. He's not unbiased.
> It has caused my depression and anxiety to worsen and I think I'm possibly burned out.
that combined with your manager saying you took the easy way out makes it pretty clear - you made the right choice.
your former manager sounded afraid. of what to do with reduced headcount.