Worried my friend is about to blow up her life for a fling

I'M worried about my friend, who's recently turned 40 and seems to be having some sort of midlife crisis.

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She's fallen hard for a guy who's 12 years younger. They work at the same place, so see each other every day. For the past few months, all she's done is talk about this younger man and how much she fancies him.

Every time we go out, he's the only topic of conversation and myself - and a few other friends - think she's lost the plot.

She has a really nice husband and two young kids, but I don't think she's aware that she could lose it all. She's admitted that her husband is suspicious, even though nothing has happened between her and this other guy.