I often see individuals who are in an active relationship. However, rather than chosing couples therapy (or given the fact that their partner will not enter therapy) they come to see me on their own.
They recognize that they have to work on themselves as they address their own relationship issues. The cause, however, of all relationship difficulties can be boiled-down to once concept - acting inauthenticity towards one's self and one's partner. It is honestly that simple. A good relationship demands authenticity from both partners all the time - but that is incredibly hard to achieve. We don't know how to be authentic and/or we don't know how to respond authentically in a relationship and each missed opportunity like this just adds to the dysfunction in a relationship.
Unfortunately though, the odds of being authentic in a relationship are highly stacked against us. Many of our interactions in everyday life are not authentic, and as children, we often learn that expressing authentic feelings often does nothing for us, so we learn to manipulate to get what we want. When in a relationship itself we often fear upsetting the other person, and in many cases react to past situations in the present, like thinking someone is picking a fight with us like they did last week, when in fact they are not. It is this kind of thinking that therapy aims to address, for the truth is that authentic relationships are much more fruitful than ones based on anything else.