Right, new name and I'm also posting this on behalf of a friend (who's here with me), who wants the MN view on this but is worried about outing and doesn't want to become a MN member herself.
My friend, who I'll call Anne, and her DH, who I'll call Mark, have been married 18 years, have 3 kids and are basically soulmates. However, pressures of work and kids and exhaustion meant that their sex life had dwindled a lot in the last 4-5 years. Maximum of once a month in the last 2 years... until, in the summer, they got an au pair. Au pair is absolutely fantastic and Anne loves her. She's also very attractive and is in her late 20s, and Mark (early 40s) clearly finds her so. Suddenly, Mark's sex drive is through the roof. Anne and Mark having sex several times a week and Mark clearly also having "me time" fantasising about the au pair as well. Anne is pleased about sex life, but worried that she should be worried. There is no real threat - the au pair has a girlfriend, Mark is always completely appropriate with her in person, etc etc. Au pair is happy and unaware that Mark fancies the pants off her.
Perspectives? Should Anne worry or not?
TIA