As far as reconnecting with that specific friend, there’s not much input I can offer there, but I’ll gladly share my feelings on boundaries in a relationship. If your partner is making a demand such as this, to cut someone out of your life entirely, then I feel you are correct that this is a reflection of your partner’s personal insecurity. A partner’s insecurity, while valid, should not give them the authority to dictate the choices you make. However, I feel like it could also be, on some level, a manifestation of mistrust that she feels towards you. If you ask me, a relationship without trust just doesn’t seem like it can be healthy, chief. Of course, this is all opinion-based, but my advice (also M21 in a committed relationship btw) is that this is going to take some serious communication to be sure that boundaries can be set in your relationship that 1. meet the needs of both parties and 2. are not harmfully restrictive. I hope this gives you something to work with, and best of luck to you!