David wasn’t perfect. He was overwhelming successful because He had God’s heart for his assignment and generation, but he had extremes in terms of his aggression and anger, lapses in his leadership, and weaknesses that discredits his strengths in some situations.
His “fatal” flaw was women. Not that David was a sex nut as much as he continued to seek the ideal woman he lost when Saul went back on his promise. I’m not being dogmatic about this, but David’s behavior looks a lot like this to me.
Consider that in his youth, in a moment of his greatest triumph as a nobody, his leader promised to give him his daughter in marriage, then reneged. Consider that David, somewhat unprepared by experience built his promised bride into an unrealistically ideal woman, a woman and ideal with which he never became one.
I think David may have been looking for this ideal woman the rest of his life. His approach to women was faulty, a tendency to objectify them and fall short of really loving any one of them without some glaring dysfunction. David never understood loving someone because of who they are. He was still attempting to impose upon them some ideal that existed only in his own mind.
Oneness of spirit is more important than oneness of soul, to be soul mates. And, oneness physically should be an expression of this spiritual unity if it is to be a completing and fulfilling aspect of the sanctity of marriage. David’s wound and trauma with Saul’s betrayal as a young man unprepared to properly measure the experience continued to be a wound and trauma throughout his life. He was marked by poor decisions when women were involved in the situations.