Adultery does not nullify the marriage. You will not find that in any biblical scripture, Christian church teaching, or legal text. Period.
DOES MICHAEL CONSIDER HIMSELF BOUND UNDER OATH TO FORSAKE ALL WOMEN BESIDES TERRI?
Such an oath is a sine qua non of marriage, at least in a post-polygny age. By his words and actions, including his declaring himself to be Jodi's "fiancé", Michael has indicated that he does not consider him to be bound by marriage oaths. Since such oaths are a sine qua non of marriage, Michael therefore cannot rightly consider himself to be Terri's husband in any but the barest legal sense.
Show me where I said automatic. You need to calm down so we can see your Christ-likeness. :)