I don't see adultery mentioned anywhere in his letter.
In the letter, Newt pledged “personal fidelity to my spouse”.
For those in Rio Linda, that means “no adultery” (except for Mormon polygamists).
Good point.... although there is some connection between infidelity and adultery, they are not synonyms. Amongst other things, if a spouse refuses to have sex with the one he or she is married to, that also is an act of infidelity.