“He Cheated in an Open Marriage” gives you a flavor of what happens when a higher-status guy is getting older and is in an “open” marriage/relationship. If a guy keeps working on his game, body, and value, his sexual market value (SMV) will outpace his wife/partner’s from age 30 onward. Or age 35 onward, depending on the couple. This produces a strong incentive for the guy to push the relationship’s boundary.
The greater the disparity between the SMV in a couple, the greater the temptation to do such things.
The venue in which the story is being published is also notable, as the whole issue is devoted to what’s happening to marriage (from women’s perspective, naturally). Under current divorce law, every woman who makes less than her partner is incented to marry that partner if she can. No woman wants to directly admit that, however.
Poly/open is becoming more common in the overall culture. Smart guys will figure out how to leverage this trend.