How awful for your daughter and distressing for you. Keep in mind that you knew nothing of what happened, and there is no blame on you, it is entirely on your daughter’s ex.
I found myself in a similar relationship at 17 (lower 6th). My bf was intense and I truly believed that I was special and it was me and him against the world, that nobody understood our relationship, I could soothe his mh issues and so on.
His control was suffocating, he bombarded me with written messages when we were apart and questions when we were together. I believed that the sex was special, but it was on his terms both psychologically and physically
.
I truly believed that he and I were together forever and had something so special. I told nobody of the rows, the sex on demand or the lurking fears when he threatened suicide to keep me in line. Certainly not my parents. I was in a bubble.
Your daughter has burst that bubble, she is strong and and you can now support her to help rebuild her life. Be strong for her and support her, but I’d advise against badmouthing her ex in an ‘I told you so’ manner as she may well still have feelings for him despite seeing the light. In my case it took me years to realise just how bad my situation had been.
You sound like a great parent, your daughter is lucky to have you.