The fact that you have not settled permanently into an unsatisfying relationship is a good sign. You've identified familiarity, security, and fear of being alone as the forces that have compelled you to linger in these relationships until they ended badly. This awareness can help you break the pattern. However, you also need to acquire a deeper understanding of the qualities you require in a partner and how to determine if a potential partner possesses these qualities before you become emotionally enmeshed. This can be a quite a challenge, especially after the series of disappointments you've experienced.
Love is a business of the heart that often requires a cool head.
This can be a close friend, a relative, or even a therapist. Try to identify such a person who might be willing to serve as your relationship coach and mentor. If you are feeling discouraged, give yourself permission to take a break from the relationship search. During this time, hopefully with a relationship coach, focus on achieving a better understanding of yourself and the lessons that might be gleaned from your past experiences. Clarity and new insights will provide you with optimism and confidence for a fresh start.