I have to ask how is this NTR? I can see it as cheating on Maddie's end yes seeing as she is sleeping with Danny while still being with her husband, but Danny didn't outright steal Maddie from him. In fact Jack is 100 percent clueless on the affair.
Most NTR dabbles in the other partner never finding anything out. There's semantics to what goes into the sub-types of NTR (netori, for example, is main character stealing a partner, netorase is the partner willingly/deliberately sharing their partner, etc), but at no point is it necessary for any character to explicitly go "I was stolen!" for it to count.
Maddie opening up the 'deal' with "Claim the entire town for yourself and I'll scheme with you behind my husband's back," still kind of did that in between the lines. Them going on to screw in more dangerous places is more apparent depravity.