As I see it Op, and drawing my own conclusions from all your posts (which I have read) it seems as if this relationship, at least on your part, started as an escape from your boredom or dissatisfaction with your "vanilla" marriage and life, and to begin with was giving you something which you felt you wanted/needed but could not get in your marriage or from your husband.
I can easily see how it could have started out as a very exciting, kinky, secret life where you could almost become someone else for a while whilst exploring your own sexuality with someone who SEEMED to want you as much as you wanted him.
Obviously it then started to develop into a more formalised Dom / sub relationship. (I assume this progression was driven by him, but that you fully consented to it?)
In his role as the Dom, I can see that he would have gradually ramped up the stakes in this game you have been playing. You indicate you had discussed safewords and hard limits, but I also intuit that he has consistently been the main one pushing you beyond these?
As you must know, regardless of whether a relationship incorporates elements of BDSM (to whatever degree), or is 100% vanilla, the keyword always is consent. And in BDSM especially it is 'informed consent' ... in other words you must know EXACTLY what he is planning to do to you so you are not surprised by any action he takes, or act he inflicts, or has you perform, in order to fully consent.
Without informed consent it is simply abuse/rape/torture.
The other thing I do know from experience is that males who simply call themselves Doms (even though a responsible BDSMer would never acknowledge them as such) often tend to escalate the stakes taking things you are doing to greater extremes. Not because YOU want to experience more, or push the limits harder, but because HE is like an addict seeking the high of that first rush he got from feeling so in control of another person (who he treats like an object) and having (at least the illusion) of getting his every desire, no matter how selfish, perverse, or extreme, satisfied on demand and to his precise standards.
But, over time, as you insist on not going further and want to stay within your limits, he becomes jaded and dissatisfied. The anticipation, the rush, is not the same for him when you are doing the same kind of things together every time you meet up. Much like having sex in a vanilla or regular marriage or relationship things get boring if you don't change it up now and again.
To this end, that is why he has recently pressured you into switching roles, with him ostensibly becoming the sub and you the Domme. It is simply just another way for him to seek out that high from a different angle. But don't be fooled for one minute that you are in any way actually dominating him. He really is the one who is 100% in control of all that you do, and the moment you, even when acting as his 'Domme', do anything that he doesn't like or enjoy, he will lash out and punish you for it.
But for the kind of man you have been involved with this boredom ultimately becomes dangerous because he won't stop until he finds a way (no matter what it involves) to experience that high again. And, because he doesn't really see you as a human being, with feelings and deserving of respect, he won't care what harm he does to you, your life, your family or your friends in the process.
His pushing to make you go further, do more extreme things, is made even more dangerous when it is combined with a naturally callous, selfish, ego driven or narcissistic personality. And being honest, from how you have described him, I would say he fits this type to a T as he, from your own posts, shows...
- no real morals, integrity or standards otherwise he wouldn't have targeted a married woman in the first place;
- knows your abuse history but shows no real understanding or compassion for it or you;
- has had multiple relationships other women whilst still seeing you (with your knowledge and not caring how that would make you feel) and then cheated on them, and you, with absolute belief he had the right to do exactly what he wanted and without fear of any consequences;
- did not want / love or respect you enough, even when you offered to leave your marriage, to commit to a full relationship with you but still selfishly demands you continue to participate in his "game"
And now, has proven without a doubt he has no consideration for your mental or physical wellbeing by physically wounding and injuring you, despite knowing he was breaking (not just pushing against) physical boundaries you thought had been agreed.
Ask yourself OP, at what point do you finally realise that all the 'care' 'love' 'attention' 'understanding' 'friendship' you think he has shown to you in the past was all a lie simply so he could get from you what HE wanted. I promise you, every time you thought he was being genuine, the times you truly believed he cared, the times he had you convinced you were soul mates, the sweet words he used to get you to agree to do what he wanted, were ALL A SHAM .. and all carefully designed and used to allow him to feed his own desires and nothing more. None of it was real.
He has covertly, and more lately overtly, manipulated and pressured and physically forced you to do what he wanted. He does not care about you one iota.
However, during all this, you have also gotten used to the rush, the anticipation, the exciting fear, the sense of almost delicious wickedness at having this secret life, the intoxicating feeling of being utterly possessed and captivated. And this is now the addiction you have to break free of once and for all.
It won't be easy. You have to face yourself in the mirror and realise that you did have your part to play in all this, regardless of how it has ended up. You have to take responsibility and be accountable for what you have sought out and how low you have allowed yourself to sink.
But, once you have done this, and truly want to walk away from this, you will be able to. You have to reach deep down inside yourself and find that strength to take the first steps towards recovering your mental health and physical safety.
I would suggest your first step towards dealing with this must be to speak to a rape crisis or abuse counselling and support service... because you have been raped!
They will be able to help you break contact with this man - although as previous PPs have said, you can start to do this now by blocking him on all media and phones, or better yet, get a new phone number and be careful who you give it to in case he can get it out of them.
They will also listen to you and help assess whether there is any risk of this man coming to your home and attacking you, or your husband, or other family or friends. If a risk is there, they will help you find the best way to protect yourself and those around you, involving the police or courts as necessary.
You could also speak to a sexual addiction support service too. There is Sex Addicts Anonymous just as there is AA for alcohol, because you need to address your own addiction to this BDSM driven rush you have had too.
From there, with a support network to guide you as to what is involved and the implications of any course of action you decide to take, I would strongly advise you to report this latest assault to the police.
Be assured the fact you have previously consented to some types of BDSM activities does not mean that this latest assault will not be taken seriously. You did not consent to his latest attack which resulted in you being raped and injured.
Please think about the fact that without your bravery this predator will continue his escalating behaviour, and I know from personal experience that this can lead to a fatality.
I honestly would also advise you to seek out a therapist who is experienced and open to dealing with BDSM related trauma as your first step in positive self care too. It is easy to feel you have done such wicked things to yourself and your husband that you don't deserve to be cared for and need to be punished somehow - but you do deserve it, and you must actively seek out ways to come to terms with any guilt, fear, shame or self loathing you may feel.
Once you can understand yourself and what motivated you down this path in the first place, you can then start to think about whether or not you need to come clean to your husband, or whether it would be better for you (and your husband who is, at least currently, totally in the dark about all this) to walk away from both this abuser and your husband and find a new, totally separate and independent life that truly makes you happy.
Finally, to address your question about whether to tell his current girlfriend right now (ie before you have been to any support services or the police), my advice would be simply this:
I would only tell her AFTER you have been in touch with the teams who can support and protect you, and if deemed necessary protect her too.
If, after speaking to them, you still want to tell her then do so by all means, but don't go into great detail, and be aware that this action will provoke him.
However, you must be absolutely committed to using the various support organisations I have mentioned above BEFORE you speak to her. Preferably have several telephone conversations with them before you decide what to do, and keep the telephone numbers you need written down and with you at all times for when you have a wobble.
But, if you have formulated some idea that just by telling his girlfriend it will provoke a situation whereby he then leaves you in peace once and for all, then you are fooling yourself ...SO DON'T DO IT!!
It is far more likely that it will provoke him into a much more serious series of actions that will almost certainly put you at great risk of further physical harm. These type of abusers do not take kindly to having their sweet little life taken away from them and will often lash out. At the very least I would expect that he would contact your husband and tell him the whole story as revenge, as this abuser will believe if you end his relationship then he has the absolute right to end yours ... and your poor husband does not deserve that.
Only with the benefit of advice and support from the rape crisis centre and/or the police, or your own therapist, might it be appropriate to tell her what risks (physical and mental) she is taking if she continues to have a relationship with him.
I sincerely wish you all the luck, and strength, in the world.
Also apologies to other PPs and MNs for the length of this post, but I genuinely am deeply concerned for the OP and wanted to try and help. If I went overboard I am really sorry.