In my case the answer was self worth. I had none. I did not believe I was good enough for happiness so I always ended up in bad relationships. I was just someone to be used and taken advantage of.
During the last years of the marriage I went into therapy. I also secretly made friends online and tried to build up my confidence and trust. I learnt to believe in myself, that I was worthy of love, happiness, peace and security. One friend in particular I continually found myself drawn to. The friendship had been there for over three years. Not a close friendship, we had never met. I trusted him and he seemed to trust me. Months went by when I deliberately did not chat with him. Something about him felt so good it scared me. We eventually started chatting more and more and sharing aspects of our lives. I felt as if I had met a soul mate. I didn't really know him from Adam but over a couple of months we grew closer and closer. He seemed to feel what I was feeling. We shared much in common, had similar ideals. I started flirting and he responded, even encouraging me. I feared that I really was falling in love, too fast and falling completely out of control. No one had made me feel the way he did. I don't think I had ever really been in love before. I did a few stupid things back then, he did a few himself.
That was a very special day. He did only stay the one night but I know he regretted it afterwards.