They are committing themselves to one person for a lifetime. Getting married doesn’t mean you die. He still looks at other people. I still look at other people. That’s the line. Going off and flirting with others, having an affair, etc., is something different – though of course if couples agree to that, I see no problem at all with it.
I can find other men attractive. I’ve even met men who leave me thinking, “Woo, he would’ve been a nice match.” It ends there. Everyone is different in how they handle attraction, and I don’t believe we’re all strictly monogamous creatures (people can be socially monogamous, sexually monogamous, etc. – monogamous is quite the blanket term).
I’d be dumb to think my husband’s never met another engaging woman who hasn’t, from time to time, given him feelings. Most of us getting married for the first time have probably another 50 or so years to go in the marriage. In the course of a lifetime, it’s just unrealistic that other attractions – some perhaps even serious – wouldn’t be there. You can control your actions…but not always your feelings. You can control, of course, how you channel those feelings.
The day will likely come when my husband has a crush on a co-worker. I can stick my head in the sand and pretend he has eyes for no other, or I can live in the real world and accept that both of us, realistically, will encounter several possible matches over the course of a lifetime. Folks we might have married, been attracted to, etc., if not for each other. The world doesn’t stop spinning when you get married.
That said, if cheating is a serious desire or if you’re otherwise unhappy with your fiance, the writing’s on the wall that it’s probably not a good idea to get hitched, at least at that time. But there’s a balance. I think the “feelings for others” thing can go too far in the other direction.
I see women on here all the time insisting their husbands don’t look at porn, don’t check out other women, don’t masturbate, etc., because they’re “totally” devoted to the wife. I don’t buy it. I don’t think the wives buy it, either. But they’re in this “either/or” black or white dichotomy and don’t see that there can be an in-between.