Hi there,
I would say you are pining, not for your ex but for the security and love you deserve after five years of being alone. Your relationship with him was obviously quite a serious one and you had a child together. Your mind is using your ex to represent the need for somebody close in your life because this is the last time you may have felt the satisfaction of being together and happy.
I hope you are feeling OK, try to stay positive and keep up the search, I'm sure you will find peace

Linzi