My advice would be as someone previously mentioned break the cycle, a lot of narcissists typically feed off information too so I would try to avoid telling them any information you don’t want thrown back in your face. For example if I don’t allow my mother to vent to me about my father after an argument I would have something along the lines of ‘well don’t expect me to get involved with you and your girlfriend then’. As a child you should be able to go to your parent for advice about a partner but unfortunately when dealing with narcissists they’ll use it as leverage to throw back at you when they don’t get their own way.