Thanks for your question. My name is XXXXX XXXXX I'd like to help you out.
In general, I would say that it is not normal for someone to leave so abruptly like that after having stated that he wanted to be with you forever 2 months before that. However, if you know that he is extremely narcissistic, that does make it much more likely that he would behave this way. Between the insensitivity for your feelings, and that he blames you for problems that he clearly contributed to, that is a combination that will most likely continue to cause him to have problems in any relationship that he enters into.
People who are narcissist have a tendency to live mostly for themselves and "in the moment." It is certainly possible that when he told you that he wanted to be with you forever that he really meant it, and then when the honeymoon phase was over he wasn't willing to put the necessary effort into work through problems and talk things out. Narcissistic people tend to be more selfish and impulsive, and in that way end up hurting a lot of people because that often causes them to have problems with any situation that isn't consistently benefiting them or making them happy.
It does seem possible that he could have Narcissistic Personality Disorder. However, even if he doesn't, what you've described is a personality type that often struggles greatly in relationships. If you've been having a hard time with all of this, or find yourself blaming yourself for what happened, I would highly recommend meeting with a therapist. It sounds like you made every effort to make this work, and deserved more than what you got from him in all of this. I definitely wish you the best, XXXXX XXXXX there's anything else I can do to help just let me know.