What you see as a negative consequence, I see as something normal. In the moment, feelings develop and are expressed. It is a passing illusion, a wonderful hallucination. You say that Ms. Gold wasn't interested in having a relationship with him, but she was having a relationship. It may not become an ongoing relationship, it may be a one time, sex only thing, but it is a relationship. The fantasy can be entirely different for both, but it is a mutually satisfying experience. Saying "I love you" to someone with whom you just exchanged orgasms is not unnatural or unreal.
My wife understood this and has described it to me what her relationships were like with married, cheating men before we became a pair. In particular one guy insisted that he dreamed of leaving his wife for her. Daniela asked why, and he said because Daniela was more intellectual and eagerly engaged in sex. Daniela had him call his wife (they were out of town in a motel) and directed him to tell her, his wife, how much he loved her, all the while Daniela was sucking his dick. They later went out to a jazz club. Afterwards, Daniela explained that was why she was in his life, their lives, because she was the other woman, to suck his dick like his wife wouldn't and go out to places his wife didn't want to go.
The wife's birthday was coming soon, so Daniela told him to buy her a birthday gift, and they shopped for it together. There was something they thought would be nice but he said was too expensive. Daniela took out her card and paid for a $600 gift for the guy's wife.
Once we became serious, Daniela agreed to my request that she not have sex with any more married men. The experiences that she has told me about made me realize that being non monogamous isn't just about the sex - it is about the feelings, the fantasies, the dreams. Both Daniela and I feel free to live those, even the irrational outbursts from time to time. BTW, I have gone on several extended vacations with a woman in our group to pursue our fantasies. Both Daniela and her husband are good with it. Daniela has never done more than a long weekend.