The thing is with abuse, it starts like a dripping tap.
You meet a great partner, who seemingly cannot do enough for you. They're complimentary, helpful, very giving in bed, generous, kind, everything you'd expect a good man to be.
Then one day, sometimes months or even years in, they insult you. Nothing massive at first, maybe they tell you your dress is too tight. You put it down to them having a bad day. They're normally so lovely. Nothing else happens for a week or two. Then they have a tantrum about something you haven't done right. Again you decide they're having a bad day.
Their bad days increase, slowly, but on their good days, they are still a shining example of the perfect man. You start to wonder where the man you met is. What went wrong?
When their bad days outnumber the good, you consider leaving, suddenly this wonderful man you met and fell and in love with is back and better than ever before, laying on compliments, helping you, whisking you away on holiday etc.
You decide to stay. They start having bad days again. Is it you? Are you doing something to upset them? They're still wonderful to everyone else.
While all of this is going on, they slowly erode your confidence and power. Maybe they 'help' you put the kids to bed, after all the kids listen to him, not you. How would you ever cope without him? Isn't he so wonderful helping you? Maybe he takes control of the finances, to help you save for X, we all know how silly you can be with money. Silly you, but no matter, look how great he is helping you.
Sally calls, you can't go out today. You've made plans/he is ill/your clothes don't fit/you've no money. He never stops you going. He would never ask you to stop your friendships, but something always seems to come up. Illness, he'll question whether you really want to wear that, you go but you feel like shit all night, next time Sally calls, you're not too keen on going out. Sally stops calling, sick of being turned down by you or having you feeling down all night because you think you look like shit.
Slowly you realise you're alone. You've no friends, you have to ask for permission to spend your own money. You're a shit parent, your kids don't listen to you. He's having bad days every day now, but how can you leave? Sally won't support you, she stopped calling months ago. How will you get the money together? How will you cope with the kids without him? Is it really better to leave?
And then all of a sudden -wham - he's back, that lovely man you fell in love with. You stay. You tell yourself it's not that bad. At least he doesn't do X. Once he does X, you'll leave.
He does X. He's sorry. There's that man again, the one you loved. X becomes Y. He does Y. Y doesn't seem that bad anymore. You're so beaten down, the abuse is so ingrained, you cannot tell what is abuse and what is normal anymore. You should leave. Is leaving really better? How will you run your own finances? Parent alone? By this time you genuinely believe you are no good at those things.
Oh look, there's that lovely man again, surprising you with flowers.