[firebrand]

By legally you mean legally in the Church. Because they could always get a divorce.

You seemed to be going back and forth between adultery and the longstanding intent to commit adultery going back to the invalid marriage vow.

[annalex]

Correct, on this topic I am only interested in the laws of the Church. American laws of marriage and divorce are a grotesque absurdity not worth trying to figure out.

You seemed to be going back and forth between adultery and the longstanding intent to commit adultery going back to the invalid marriage vow.

These two are different things. Adultery is a sin that a married person may commit. Invalid marriage happens when there is one or another defect of ability or intent, lack of monogamous orientation is just one of them. I'd be happy to explain if you frame a concrete question, in a day or two. I'll be off for a few days.