More than likely your emotions like sorrow, grief or anger are flying high.
You need a steady ear that can give you rational and comforting advice, or at least an unconditional purr.
It's common for us to compare new people in our lives to our exes, or to build a wall of safety around our emotions. And of course, we've learned many lessons from past.
A little caution is a good thing, but sometimes this can develop into an emotional shutdown.
No new person will be good enough or as good as your ex if you place your ex on such a high pedestal that no one else can reach it.