What you described doesn't necessarily indicate OCD (Obsessive-Compulsive Disorder) but could be related to a psychological phenomenon known as the "Zeigarnik effect" and personal preferences in reading habits.
The Zeigarnik effect refers to the tendency for people to remember and focus on unfinished tasks or activities more than completed ones. When you start reading a series or book and leave it unfinished, your mind may subconsciously hold onto the desire to complete it, creating a sense of unresolved tension. This unfinished business can make it difficult to fully immerse yourself in other books or series until you complete the previous one.
Additionally, personal reading preferences can play a role. If you are invested in a particular story or characters, it's natural to want to see it through to the end, even if you acknowledge that the series or book isn't particularly well-written or enjoyable.
It's essential to recognize that this phenomenon is a normal cognitive process rather than a symptom of OCD. However, if you find that this tendency is causing distress or interfering with your daily life, it might be helpful to explore your feelings and habits with a mental health professional to gain a better understanding of your reading preferences and behaviors. They can offer guidance and support to help you manage your reading habits in a way that brings you satisfaction without causing undue stress.