I don't think this counts as NTR. The guys gone for half a year? No calls? No visits? If you abandon a car in the middle of the street with the keys in the ignition and motor running? You should expect someone else to drive off with it.
This is total NTR. bitch is a horny, submissive slut who doesnt care as long as she gets dick. Her fault for getting involved with such a perverted scumbag.