The nice "most of the time" cannot make up for the % of time he's not nice. Look at how appalling he's made you feel in a "not nice" moment- and it sounds like he's been undermining you, too. That's really not nice. That's calculated. It's also part of the pattern of abusers, I hate to say. Can you even him or bear to be near him knowing he could just turn on you again? I'd be kicking him out now for my nerves and sanity. At the very least, this lightening turn around seems unreliable and he should move out to try and work on the relationship- if you want to.
As a pp said, if you feel you can stick to it, could you smile and fake it, welcome him back, take a week or two to set up everything you need whilst playing nice, arrange for some support to be at hand and then tell him to get out? With your dad and/or sister there to back you up? If you feel safe to do this, it could buy you time to think. But only if it's safe and you will stick to it and can fake it. Whatever you do, don't agree to ANY childcare arrangements whilst you're not feeling clear headed and don't let him dictate them.
Lots of new mums struggle. Even the seemingly all in control ones. It's not just you. A quick flick through the forums here or similar sites and even articles in the papers or mags will tell you it's not just you.
No matter what you choose, I hope it all works out for the best. Personally I couldn't forgive or trust; I'd boot him right now, but I'm not you. Good luck xxx