caught red handed on the phone!!

I received a phone call from a anonymous caller (private number), a girl that i did not know or recognize her voice, anyway she called early one morning to say that my partner had gone off with a girl across the road to the beach in her car, i texd him to see if he was with another girl and he txd "no of course not i,m in bed honey, goodnight xo" so i called and the phone that must have answered by accident, he had no idea i was on the line and i heard everything that she was doing to him in the car.
Not men are all the same but please do not lie. .
its hurtful, its not nice and now i cant even look at him straight without picturing what he was doing with this other girl.
don,t give anyone the time or day if they ever do this to you