it's very difficult. The moral part of me would want to tell, but the rassional one thinks that if you tell you could break up a marriage that otherwise might not end. What they're doing is dispickable, but maybe it's just a fling, maybe they'll go back to their respective partners, never stray again, and the partner will never know and thus never get hurt. If my dh had an affair and it had ended, I'm not sure I would want to know, purely because it would wrip my life apart and that of my ds. If they have plans to be together and leave their respective partners, then ultimately one of them will tell.