Found this in Psychology Today --seems relevant to your question. Here's a snippet from the middle of the article. It goes on to explain further.

"However, the explanation for deliberately hurting the person you love is far more complex. Certainly, one major factor in hurting the beloved deliberately is related to the central role that mutual dependency plays in love."

[link to www.psychologytoday.com]

Found a cool site with recording of Willie Nelson singing "You Always Hurt the One You Love", but got a GLP warning in red letters about posting copywrited song lyrics. Oops!
Here's the site minus the song; you can look it up.

[link to www.elyrics.net]