A narcissist will always give you ultimatums and judgements about your isolation from others(in case he has already discarded you, otherwise the ultimatum will be about leaving you). For example, saying things like “You will be left alone in the end and nobody is going to love you”, etc. etc. A narc thinks that he has become god and whatever he’d say or wish, will happen. And he does so in a way and from that place from where nobody else than you and him can know about it, so that when you talk about it to a third person he can say that you are just suspicious. This is referred to as Gaslighting. Watch the movie ‘Gaslight’ if you don’t like to read much. It has been depicted in that movie quite well. This is basically to weaken somebody’s mental strength, so that one begins to doubt himself/herself and ultimately the narc can take advantage of it and make the victim his puppet.
I Think For All 