One of the reasons why men have an interest with another woman and not his own wife is because he lost all interest in his wife. Things are probably boring in every way no matter what. No spice in the bedroom, no new hobbies, going out, doing things together and so on.
The spouse gets an interest that attracts them by another person that they have not had at home lately or in along time. Example: Sex. If you haven't given it to him lately and he may have been under stress. If he doesn't get it from you then he'll get it on his own from somewhere else. Its the same woman would probably do. If she doesn't get it from her man, she'll go somewhere else and get it from another man. Men release their stress by having sex; after that they feel happy and relaxed. It's not only sex itself, that goes along for things being done during sex. Doing new things will make the attraction last longer. Also things he likes and things you like.
To say it in a blunt way. You're boring so he found somebody new and exciting. Possibly younger who is more attractive. Somebody boring will make him boring, someone who is fun and energized will make him the same way. Whatever the spouse is like rubs off onto the other person.
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