Who’s really at fault?

A couple in a “situation-ship” is beyond toxic at this point. This woman has given, given & given this man everything from sex on demand, money, several years, children, threesomes, etc. In the end, he still never has dated her & got engaged to someone else. She still gives him whatever whenever & he just takes it without hesitation. They’ve had numerous fist-fights & both speak to each other like they’re absolute shit-yet still deal with each other. Who’s at fault for this mess-him for using her & taking, or her for giving & allowing him to treat her this way? My husband blames him & I blame her…we both made valid points so now, I wonder what others think 🤔