i have this constant feeling of being inadequate

Whenever I am in a relationship, especially a romantic one this feeling goes the roof, and often I have to say to myself "that it is not real", until eventually, something happens that shatters me to the core, and it takes me such a long time to recover.  


I don't want to experience that again, I don't want to shatter my reality again and start from zero again, not knowing who am I or what is my value.   


Am I a coward? Does it make sense to live "alone"?