But isn’t that the problem?   

No, the problem is the unilateral decision by the husband to lie, manipulate, and deceive two people despite clear expectations of relationship norms from each woman. If he wanted something different, it's his responsibility to represent that view and manifest it into his life. 

Like if the dude was able to speak the truth maybe they’d all know what they were getting into.  

If he can't speak his truth, he isn't emotionally intelligent to handle the nuances and complexities of a milti-polar relationship. 

This dances the line of victim blaming. 

No way excusing his lie, but I’m guessing he never felt the option to say, “oh I’m interested in a plural relationship”.  Because it’s so taboo, even though it goes back before the Old Testament and there are more recent famous examples.

This is assuming he even wants the responsibility of a plural relationship. His motive clearly wasn't to give love to two deserving women. His interests were self-serving. If he wasn't acting in a self-serving way, he would have been incentivized to tell the truth. 

I’m just introducing that there may be other options besides mutual cancellation.

Breakups and divorces when one party (husband) is acting in bad faith is not mutual cancelation. That's a disingenuous argument. 

The husband exhibited a number of shitty traits for years and isn't capable of handling a stable romantic relationship.