My wife suddenly started going out with her "friends" until all hours of the morning, lost 30 pounds, got a tattoo and a tummy tuck, and texting all day and locking her phone so that I couldn't see them. I asked her if she was cheating, and she said "no," so I believed her, but I firmly told her that I would NOT tolerate any infidelity.
She seemed to get the message, told me she respected my strong stand, and now she comes straight home from work and we've been happily married ever since.