If they're going to stay together, I'm surprised they're not getting marriage counseling. They should be doing something to improve the situation. Maybe this dysfunctional dynamic has become their new comfort zone? It's what they're used to, change is scary and it seems safer to leave things as they are. Could also be a Mexican standoff: Neither wants to be "the bad guy" who spearheads a divorce.
What are some of the effects all this has had on your relationship with your partner (the one who's in this bad marriage)? Does he get upset a lot?
Love means never having to say, "Put down that meat cleaver!"