DnJ and I have, like all of the other posters, have experienced some very difficult things when it comes to MLCers. They do not operate logically. Everything is emotional for them. They are like 13 year olds who have hormones going nuts full throttle or better yet, 2 year olds that are going through that period of time. They are depressed and do not understand why they feel the way they do. They lash out at others because they are the people they feel safest lashing out at. None of this is personal towards you and your child.
Can any of this beahaviour be a sign of narcissistic personality disorder. It's based on stunted growth at age of 2 where they had a problem with lack of affection in early formative years. They basically have a hard time developing their own identity and create a false sense of self, aka a mask. They project their inner selves onto partners and treat others as objects or sources of supply to feed their ego. They shower their partners with affection in earlier stages and thrive on the honeymoon phase. When the relationship gets further down the line and a deeper bond is needed they tire of their partner as they start seeing their flaws and the image they created of their partner from early on doesn't match the person in front of them. This is when they begin demoralizing, devaluing their partner until they can find a new source of affection or supply. They tend to discard someone no matter how long they've been together and start building up the new partner. It's a cycle for them. Dr. Ramani and Dr Sam vaknin have great videos explaining the psychology and the behaviors of someone with NPD. It feels to me a lot of us are on the same boat and we are dealing with people who are innately broken and lack empathy for others, their world revolves around their needs and they see themselves as flawless.