“Why Do We Always Hurt The One We Love?”
Canadian pop singer Dan Hill (popularly known for his song, “Sometimes When We Touch”) asked that question in a song with the same title. The Mills Brothers, “an African-American jazz and pop vocal quartet of the 20th century,”  also asked the same in one of their songs.
You always hurt the one you love, the one you should not hurt at all; You always take the sweetest rose, and crush it till the petals fall; You always break the kindest heart, with a hasty word you can’t recall; So if I broke your heart last night, it’s because I love you most of all. 
So, why do we always hurt the people we love? In the Psychology Today website, Jewish philosopher Aaron Ben-Zeév answered why.
Lovers can easily hurt the beloved without intending to do so. Because the lovers are so significant to each other, any innocent remark or action can be interpreted in a manner that the other person did not intend and hence be hurtful. … The more time two people spend together, the greater the likelihood that this will occur. 
In his “Respectable Sins: Confronting the Sins We Tolerate,” Jerry Bridges wrote that we usually see this tendency to hurt the people we love the most when we are impatient and irritable.
We tend to exhibit many of these [respectable] sins most freely in the context of our own families. … we can put on our “Christian face” outside the home, but with our families, our true character often comes out. … While impatience is a strong sense of annoyance or exasperation, irritability, as I define it, describes the frequency of impatience, or the ease with which a person can become impatient over the slightest provocation. 
For example, we become impatient and irritable when we are running late for an important appointment and our spouse seems to be taking his or her sweet time in getting ready. We also exhibit it when we see our pet peeve such as our children biting their nails.
But according to what was dubbed as “the love chapter” of the Bible, “Love is patient… it is not irritable” (1 Corinthians 13:4a, 5b). Proverbs 19:11 tells us, “Sensible people control their temper; they earn respect by overlooking wrongs.” (NLT, emphasis added) To overlook wrongs does not mean we condone sins. It means one is patient and not irritable even when others offend them.
A prudent, patient man is not easily upset by people who offend him; in fact he overlooks offenses (cf. 12:16), knowing that to harbor resentment or attempt revenge only leads to more trouble. Overlooking them is his glory, that is, it is honorable. 
“Slow to Anger” Step
In the discussion guide of “Respectable Sins,” some of the questions are,
In what ways do you tend to express impatience? How do these expressions affect those people who are objects of your impatience?
One of the best ways to answer those questions is to ask the people we tend to hurt the most, that is, our family. Listen with humility. Avoid becoming defensive. Ask for forgiveness afterwards.
 “Mills Brothers,” Wikipedia, https://en.wikipedia.org/wiki/Mills_Brothers, accessed February 4, 2016.
 Aaron Ben-Zeév (9 October 2010), “You Always Hurt the One You Love,” Psychology Today, retrieved from https://www.psychologytoday.com/.
 Ibid. Emphasis added.
 Jerry Bridges, Respectable Sins: Confronting the Sins We Tolerate (Colorado Springs, CO: NavPress, 2007), 115.
 Sid S. Buzzell, “Proverbs” in The Bible Knowledge Commentary, Old Testament, Eds. John F. Walvoord, Roy B. Zuck and Dallas Theological Seminary (Wheaton, IL: Victor Books, 1983, 1985), 946.