LADIES...ok, why are ome women so insecure? Especially if they have been together for so long?

Why do some women tend to be so insecure? I have been married almost 17 years, and I am not like this. was maybe first 2 years, if even that. I have a friend that has a guy who is her best friend, and has been for most of her life, and they are not able to speak, or go out as friends, let alone visit. BC his spouse will not allow it. In my opinion, I think she is insecure, and maybe jelous. They have been together long enough for her to know other wise, but she apparently does not. I know they have given no reason for her to be like this, and they have never been romantic with one another. Her spouse is ok with it. So am I maybe missing something? She asked me for advice, so I am recruiting help.