I feel reasonable in asking that he not socialise with these women, no matter how low level. Am I unreasonable?
Would it make you feel any less insecure if we said whether this was reasonable or not?
Insecurity and trust is the issue that needs to be addressed here. It is about how you feel about it rather than what is actually happening or not. You can go round in never ending circles trying to constantly draw ethical lines in the sand, Your inner feelings and emotions will simply ignore these lines in the sand. then you end up feeling guilty because your feelings dont align with what others tell you is logic.
If your feelings tell you this is wrong, and we say it is not, then we are just invalidating your feelings. You then feel worse.
What can
you do to stop you feeling this way? Making demands wont do it.
If you need him to stop social contact, then that is what you need, no matter whether if its reasonable or not. It is up to you whether that is the answer or not, or is that just a symptom of deeper mistrust and hence wont really resolve the issue for you?
Finding the real core issue for our feelings is the first step towards recovery, jumping on symptoms just drags it out.