Imagine thinking you being more resistant to disgusting acts means you are superior, stronger or better than any other person. Other people just have different opinions and it really isn't that hard to believe that.
God! If you believe your relationship leads to nowhere, then break up or have a serious talk. At least her ex had enough common sense. And he had the right thought. Boy, that girl is easy. "I have a booiiifwieeend!" "I'm married with children" <- Those lines made me crack up.
But now really. That's just plain cheating, no ntr. She didn't love her ex anyway anymore and he broke up, so there hasn't been anyone stolen. EDIT: UHH!! Maybe her mangaka fucked her boyfriend behind her back and that's where the ntr is hidden. I wonder what happened on the other side of the line. Ch 3?