Women say “stop being insecure” to keep you from pointing out the insulting, disrespectful things they do to harm the relationship. Remember: this isn’t a matter of your need for her, it’s a matter of her respect for you.
The key is to tell her what she’s doing wrong without phrasing it as a Demand or Ultimatum. When she says, “I’m going to have coffee with so and so, and he’ll show me some sights around town,” say, “You shouldn’t date other people when you have a boyfriend.”
She might try to argue, “it’s not a date.” “Great, then I can go with you guys, right?” “Um, er, . . . no, blah blah.” “So you need to be alone, so it’s a date, so you should break up with me 1st.”
Just calmly explain to her what you need: which is respect! If you can’t get it from her, you’ll get it somewhere else.