I remember an identical thread to this one being posted some time ago. The poster of that thread got some quite nasty comments as well.
I don’t know if you’ve done the right thing for you. I don’t think you’ve necessarily done the right thing for your DC, your SD or your DH though. Your DH will come to resent you eventually because you will be seen as the reason that he can’t have his DD in his house, your own DC will learn of how you’ve treated their DS and will wonder if you’ll do the same to them - this is basic human nature and make no mistake, your DC will find out eventually.
I just find some of the details slightly odd. This decade of abuse? How long have you actually been in a relationship with your DH? I’m assuming that you didn’t meet on a Monday and marry on a Tuesday? So you’ve either been married a decade and dated prior to that, or you’ve been in a relationship for a decade, married for an undetermined amount of time and your DH introduced you pretty quickly to his DD. The answers to these questions are quite important I think for context.
If you met DH only a decade ago, and you've been on rocky terms with your SS for the whole time, that speaks of dysfunction within your relationship with DH and his relationships with his ExW and DD. You should never have been introduced to your SD so quickly after starting dating your H.
However, if you’ve only been married for a decade, then one would presume that you met H’s DD prior to marrying him. How was your relationship with SD back then? It sort of defies belief that a 7 year old child could mete out torrents of abuse unchecked by her father and if she did, then her father is to blame, not her mother who was presumably absent from these interactions.
It sounds to me like this child has been pulled between two parents and I doubt that the blame is only with the mother.
I’m also unsure as to how the ExW is able to just walk into your home without knocking! Does she have a key to your house? Or are you just leaving the front door unlocked or open? And she’s been barging in for 10 years? Why on earth didn’t you draw a boundary 10 years ago?
It’s easy to say that you are the bad guy, but relationships, whether parent-child, spouse, or friendships are rarely black and white!
A PP posited that children don’t have a home with both parents, but a home with a primary parent and then a weekend home with the other parent. I feel like that’s the wrong way to think of things, and I also think that this idea of one parent having the child for 12 days, whilst the other has only 2 days out of every fortnight is also wrong.
I've known divorced parents in the UK to do a week each but it seems very rare. The advantage is that the children are more secure, after all it takes a village, and this idea that the child doesn’t really have a home with e.g. the father is thrown out. It’s also harder for one parent to be accused of brainwashing or manipulating the child when time is literally split fairly. Children can be resilient and the children I’ve known with this model of truly shared 50/50 custody haven’t been confused, or felt like they didn’t belong, or felt unloved, but the opposite. They’ve known that both parents want them, and love them, and they have choices because they have good relationships with both parents.
I hope that things work out for you OP, but having seen a lot of life, I think that it may be that this decision to move your SD out of your life will come and bite you later.