Oh OP my heart aches for you, you are worth so much more than this. However, if you stay with her, you will be convinced by her that you aren't worthy, no one else would ever love you, you are lucky to have her etc etc.
I was in a long term abusive relationship and like you there were some incredibly amazing times, and he was really lovely at times. But I came to realise it was only when I was being subservient and 'the perfect wife' He was happiest and nicest when I was saddest and most repressed.
In a genuinely good, equal and balanced relationship ALL times are good (even the tough times) and both people are lovely ALL the time.
Please be fore-warned that if she gets wind that you're going to end it, the abusive behaviour might ramp up. So, get things ready first
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ensure all passwords/logins are changed to your banking, social media, phones, laptops/PCs and tablets etc
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hide, or remove from the home, important documents and ID for you and your Children
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hide, or remove, spare car and house keys. Change house locks also ASAP as she probably has a spare of the one she uses. If you can't change them immediately put a chain on the front door and leave by the back door (most people don't carry a back door key with them everyday, hopefully she doesn't)
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consider contacting your local police to make a statement about her abuse. I did this shortly after ending my marriage when I realised he'd fitted a tracker to my car. Just by making a statement and them being aware it was domestic abuse meant that the police came to do a safety inspection of my house, advised me on actions to take if he came round and also flagged my name, phone number and address as a priority should I ever call 999. Proved invaluable several months later when I realised he was attempting to break in in the middle of the night. Police were there in minutes to arrest him
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delete any private or intimate photos there might be of you to avoid any 'revenge porn' activity by her. It's a crime now which might put her off, but believe me it's incredibly embarrassing and humiliating if these images are forwarded to your colleagues.
Ideally it would be good to end things when you are out somewhere so you can just leave her and get home alone. If you live together have an overnight bag of her belongings packed up ready and tell her you will pack and leave the rest outside.
DO NOT BE FOOLED by the tears, faux apologies or threats to self harm. It's all crap.
Please get rid. I stayed far too long and it wrecked my confidence, self-esteem and mental health. I'm still recovering 6 years later.
Wishing you well with this. You and your children deserve better. DO NOT blame yourself either - people like your partner and my ex are accomplished liars, manipulators and head fucks. It is THEM and not you with the issues. You will meet someone else who'll love you, you are worthy, decent, kind and loving.
It's THEM not YOU.