The punting phone lives in my desk at work, tescos sell 'party phones' for less than a tenner, hell there almost disposable !
If I couldn't keep it at work, I would hide it at home, with the sim removed and hidden elsewhere. If it ever gets found, it's a backup phone.
Store no numbers on the punting phone, don't turn on or answer the phone unless on the way to a punt.
Sounds paranoid, but in your situation you should be. Losing your missus and kid over a shag is not worth it, minimise that risk to the tinyest percentage by being careful, it's not difficult.