mab,

You wrote, Unless it's happening in the gym but surely there are other people around.

My experience with "trainers" is that they are often untrained egotists who believe their own healthy physique somehow qualifies them to train others. They work for fly by night companies which come and go and often appear to constantly be on the make for new female recruits.

I would also suspect you are dealing with a serial cheater here who uses his profession to go from one woman to the next so he is well practiced and knows how to avoid detection.

Do not let on to anyone, especially your wife, that you are gathering data. They will try to spin a story that you are a crazy jealous husband. If you get evidence present it to OMW, other mans wife, before you confront OM. Do you have access to the cell phone bill?

Put a voice activated recorder in her car, hire a PI to observe their interactions at the gym, if you have a friend who goes to the gym perhaps he can spy for you.

God Bless
Gamma