nhwm- sounds like there is a lot going on, with the substance use, triangulating, violation of trust.. not sure if this will help you at all, but there are some older books on transactional analysis that I’ve found to be very helpful. The Games People Play, the Games Alcoholics Play & The Roles People Play. Written in the 60s, so the examples given are rather sexist and outdated in the books, but the basic info on dynamics between people is still relevant today, I think.
Basically what the books are saying, is as an adult, we have 3 states; parent (nurturing or controlling/ critical), adult (grown up rational person), and child (natural, little professor, or adaptive). These roles play out in interactions among people all the time, but with active addiction, you basically have someone who is in acting out/ rebellious, “child” role, which then oftentimes ends up putting the spouse in the “critical parent” role. Once you become aware of how this works, sometimes it can help you, at least in terms of your own behavior from your end.. However, if you have a person that’s so full of drama, I think the author says sometimes it’s better not to engage with them at all. A lot more to it than that, but I’ll post a link so you can read about it (some good videos on YouTube explaining it too). I know it doesn’t lessen the hurt of being cheated on, or exploited and betrayed, but maybe reading how the dynamics play out my help you a little: Transactional Analysis