It's not easier though, you're miserable in this marriage.
Leaving would be tough for a few months but then your life will be relatively free.
His mum is a bs excuse to abuse. Unfortunately many men take a few years to show who they really are. Marriage and pregnancy can be key times where they drop their mask.
Why are you not comfortable with the idea of divorce? You need to get to the bottom of this.
Do you believe he'll change back?
He won't. He was never that nice guy. Sorry. It was fake in order to reel you in.
Do you believe divorce is failure?
The only failure is choosing a man who hates you over learning to choose and love yourself. Life is a lesson. It'll repeat these hard lessons until you make different choices. Choose you.
Do you think 'my daughter deserves a family unit'? Your daughter deserves a happy mother, free from abuse. She deserves to know women aren't doormats or punching bags for damaged men.
Do you think you won't cope single?
It sounds like you already do! And with him gone you'll get extra things like discounted council tax and, CMS. And not have to walk on eggshells your whole life.
Do you think he'll make it difficult to coparent if he leaves? He may well do. But that's why you read up on how to coparent with a narcissist successfully. And techniques you can use like grey rock. It's never wise to stay married to the devil just because you fear being in his path. You are still his target, every day, the devil will never be kind to you. Not unless it's part of the con.
Are you worried what other people will think? Perhaps because they all love him and think he's perfect? All you need to say is 'we just weren't/aren't compatible anymore'. No one has to be 'the bad guy'. Sometimes things just don't work out. And that's ok. You can even say that last whole sentence to anyone who seems critical.
Get comfortable with the idea of leaving him. It'll be the best thing you've ever done.