I think what some PPs are missing is the fact that this kind of pseudo BDSM relationship, which has a very insidious and yet seductive and addicting thrall to it (especially in its early stages), can be extremely difficult to get out of further down the road, moreso as the severity of the manipulation and abuse ramps up. Often the victim (in this case the OP) tries multiple times to reset or renegotiate boundaries and/or withdraw from the web of intimidation, abuse, lies and manipulation perpetrated by the abuser. However, the abusers are adept at intimidation and experts at using fear to paralyse their victims, leaving them feeling incapable of making any meaningful and effective decisions towards actually escaping the abuse.
Victims will often express hopes such as "I could keep going through it if he just eases up on me a bit" or "I can keep playing this game if he just shows me he really cares for me." But of course the abusers don't ease up, and they certainly don't care.
This victims mindset of trying to barter or negotiate better treatment because "I don't have any real power to decide things" , combined with a historical acceptance of their designated (and initially welcomed) submissive / obedient role in this relationship leaves the victim feeling emotionally torn and especially vulnerable to the abuser to exploit.
This is especially true if you are not very emotionally robust, which it is clear the OP is not due to past SA experiences.
This is why people find it so incredibly hard to extricate themselves from this type of abuse. I really wish it was as simple as "block him and ignore and move on", but emotionally the OP has been so thoroughly conditioned to not see that as an option, to believe she does not have the power to impose her will over his, that even now, she is paralysed and simply waiting (fearing) for his next contact, instead of actively seeking her escape.
Also, I don't think anyone can deny there are some parties involved (OPs husband and current girlfriend of the abuser) who are either wholly or largely ignorant of what has been going on, and that will, at some point, need to be addressed by the OP both directly and indirectly.
Clearly the OP will, at some point, need to make a decision about what she wants the outcome of all this to be, beyond the simple solution of having nothing more to do with this rapist.
Then she will need to decide whether that includes telling her husband and then trying to rescue that relationship, or eventually concluding that it cannot be saved.
I agree with PPs that we know very little about what calibre of man the OPs husband is, and how he would potentially react if, or when, he is apprised of what has happened. We can only hope that he will have enough courage to look beyond the simple but brutal act of betrayal that an extra marital affair represents and see that the OP has been a victim, albeit an initially ignorant but willing one.
Equally we need to hope that whatever information is eventually given to the girlfriend about what type of lowlife her boyfriend is, will lead her to make the sensible decision to walk away as quickly as possible. Although, given that the OP has already stated that the gf has been warned about his behaviour by someone else (not the OP) and yet is still seeing him leaves me feeling somewhat doubtful that she will make her escape before she too suffers some kind of abusive treatment from him.
All in all it is a sorry tale, and my heart goes out to all involved ... barring one person of course!