Non-marital sex vs. living together

[Spanish1]

I have a friend who is not living under the same roof with a Jewish man who evidently is not observant but they are having relations. She has said that she is not interested in sex. However denying a man this access seems to me to be cruel and at the same time a way to draw a Jewish man away from his religion. Why would a woman get involved with a Jewish man when she says she can take him or leave him? Seems like some sort of unconscious punishment.