The third story 偽りの誠, is a good example why you can never take women with wedding rings in hentai at face value to slap the "cheating" tag right away, you gotta be able to read the story to confirm it; here it ends up being a twist, a scammer impersonating a childhood friend that never existed, pretending to be a troubled wife seeking some help.
Wedding rings in hentai, and porn jn general, might as well be a fetish item, the woman may be married, may be a widow keeping the ring for remembrance, may be a divorced woman keeping the ring to ward off other men since she is tired of relationships for now, etc. I have seen all aforementioned examples.
Then there's the bizarre cases where the woman is married but she is not wearing any ring, not because she is a common law partner, thus no official marriage, or doesn't love her husband anymore, the ring isn't on just because. Those are the ones you need to read before identifying it, especially when the husband is only mentioned through dialogue, without making an appearance.