well, you can sorta consider it netorare if you follow netorare's definition, which is simply your lover sleeping with someone else, which could be classified as type a,b,c... differing levels of consent. its a matter of perspective, so if you're stealing someone's lover it would be netori, which e-hentai doesn't really use as a tag, so 'cheating' becomes a better fit for that.
Initially, she was blackmailed (which is actually pretty common theme in some ntr games, and usually end up with victim giving into and getting addicted to pleasure), but she DID do a penis comparison, saying their cocks were twice as large as her husband's (male protagonist humiliation also common in ntr, although the husband wasn't shown here). she also initiated asking for anal, and towards the end she was really just lying to herself because her reason for engaging in the sex act shifted to pleasure; compared to the beginning, she was only giving into blackmailing to protect her husband. If this isn't netorare, i don't know how else to tag it.