These aren't ordinary men. They're men who've been famous since they were in their teens, had more money than they can spend since then, and both Ronan and Mark were constructed as sexless 'cute' pretty boys in the most successful years of their lives. Mark Owen has the 'I'm really a musician, nobody understands me' complex that so many ex-boy-band members seem to have, and it doesn't seem all that weird that he would get a bit lost when his whole life the entire world has told him he's the sweet, monogamous type. Maybe he never was, or maybe he got confused about who he was aside from all the constructions of him he has to live with in order to be successful. And it seems to me that a lot of footballers are ill-educated, spoilt, stupid twats!
I agree with an early poster who said it's patronising to say that all men would cheat. Chris Rock's 'a man is only as faithful as his options' is a funny and clever line and it might be true for some men, but I know a lot of lovely men who are in love with their wives/girlfriends and just aren't interested in anything else. Plus, basically everybody hhas the opportunity. You only have to go outside your house and you can find someone if you want to.
I include my own DH in the non-cheating camp - we've been together 12 years, since we were 16. Often when we were younger I said to him he might get itchy feet because he'd only slept with one person, but he won't have it - he didn't set out to only sleep with one person, but he's happy as he is. I'm not saying he would never ever cheat, but I'd be bloody surprised if he did. There are other men, like my own dad, who I totally expect to be cheaters. DH's father has been monogamous for thirty-five years and is head over heels in love with his wife. He's just not interested in being with anyone else. He's focused on her and on his family and anything else would come second best. I also know men who have been cheated on and find cheating abhorrent for that reason. I know men who have been heartbroken when their girlfriends have left them because it never occurred to them to be with anybody else but that girl.
The thing with the newspapers is once they've found a successful story they just keep telling it, over and over again. Unfaithful men is a hot topic right now, so they just keep inserting new names and telling the story again. Probably in a couple of years a big story will break about a very famous woman cheating - and then we'll get a flood of stories of the same.
Men cheat, women cheat, everybody is capable of cheating. But there are plenty of people who don't want to cheat, and who don't cheat, and who are capable of not cheating too.