i m the responsible one. craig melvin: a working mom, new at the office. she loved her job and really loved her handsome, young boss. the thing that i never wanted to face was the hurt that i was going to cause. craig melvin: a passionate 9:00 to 5:00 affair. the problem she was married. and so was he. i grabbed his face, and i was like, you know what, i love you. i m not going anywhere. just tell me what s happening. craig melvin: cheating husbands, scheming wives suburbs are full of secrets. but being unfaithful to your spouse isn t a crime, is it? that would come next. it was just like every emotion possible all in one second. i went, [gasps], oh my god. craig melvin: murder in the dark who was behind it, and who would pay? when you see him on the video, he s armed and ready. craig melvin: two couples, two families, and the single moment that shattered it all. i knew, one day, that this was all going to come out. hello, and welcome to dateline. it s a cautionary tal