It does annoy me when people blithely blither on on threads like this about "how much happier you'll be" if you separate and how the kids' happiness will automatically follow from this. It does not necessarily follow that leaving one unhappy situation will make the OP happy, nor that her happiness if achieved will fulfil all her DC's emotional and practical needs. It's such an individualist mindset. And I'm sorry but I often think the divorced parents convinced their kids are "so much better off" are telling themselves what they want to hear.
The truth is when a relationship is breaking down and children are involved, unless both parties are total saints about it and prioritise the children's wellbeing above all else, there are only an array of bad options and an attempt to choose the least worst one. And whichever you choose may turn out to have been the wrong one for one or some or all the kids.
It really isn't as simple as getting rid of the unsatisfactory partner, instant happiness for OP, kids delighted. The unsatisfactory partner is still the kids' father (an unsatisfactory one, in this case). The kids will either have to be shared with him on a regular basis (lives split between two homes, less money all round, possible stepparents/blended family issues, missing each parent when with the other) or they will be dropped/sidelined and have to deal with that rejection head on at a young age. Moreover it's easy to imagine the only thing stopping the OP being happy is her crummy relationship - but who's to say there aren't other mental health/self esteem issues at play which have LEAD to this dysfunctional relationship? My mum left my abusive dad, but she was never happy. Went from bad marriage to bad marriage, because she was fundamentally broken long before she picked my dad and had kids with him. So their divorce didn't have me and my sister skipping around in the meadows anymore than their cluster fuck of a marriage had. Moreover my dad then got together with my stepmum, and while they did stay together, their relationship with each other and with each other's pre existing children was rocky and difficult. I'd say only my half brother (both their child) emerged from that household unscathed of the four children that lived in it. So staying together isn't necessarily a fix all either, no matter how martyred you are.
Like the man said, they fuck you up, your mum and dad. If we've chosen badly when choosing someone to have kids with, that's on us and we have to own it and make the next choice in the best possible interests of the kids we made, while accepting that there may be no "good" choice. All this "LTB and you'll be SO MUCH HAPPIER and of course your kids will be too, happy mum means happy kids" bollocks is magical thinking in the vast majority of cases.