Should I leave my wife?

During an office pool party where everyone was feeling a little tipsy, my wife of 12 years at the time put her hand on the backside of a gentleman (attractive stranger) ahead of her while climbing the stairs to an inflatible water slide. I saw this, and I harbor distrust. She hasn't apologized nor admitted fault. I do not trust her and realize that this will surface in the future. By the way, we have two beautiful daughters that adore us as we do them.