I hear you bro, but... having talked to the girl, I have to say, I wouldn't categorize this as sexual assault.
I mean.. she didn't say "yes" to a gangbang, nor did she imply or make it seem like "hey this is something I want to do." She reluctantly agreed to fuck another guy because her boyfriend pressured (coerced?) her to do it... Now, that's unethical on his part, and in a big way, but, I wouldn't categorize that as sexual assault, I mean, who's the attacker in this situation? It's an ethically grey area but not one that I think overlaps with sexual assault.
And as far as the gangbang, well, she didn't have to go along with it; they didn't force her.. Another guy walks in and starts kissing her and then pulls his dick out.. she puts it in her mouth.. that's not assault... She simply debased herself; and even she wouldn't call it assault.
After the fact, and I know you're not supposed to ever say this about a rape or sexual assault (but I'm not categorizing this as that), but, she enjoyed herself. I mean, she told me she hated herself for it, but she also consented to it and enjoyed it. Afterwards, she was basically a closet nympho, hence coming at me and my girl in secret and having no problems from then on cheating on her now husband....
Simply put, she lost all respect for the man -- yet married him still, and had a kid with him. But if I had to guess, she's probably still fucking other dudes either behind his back or with his knowledge because she was never the same afterwards.