A typical narcissist is always in search of the narcissistic supply. So, as the relationship is fading now, the narcissist suffers the lack of the narcissistic supply. The lower the narcissist feels your value, the lesser your relationship strokes his/her ego.
Thus, the narcissist constantly starts searching for a new narcissistic supply. This is generally a new partner or a new friends with benefits relationship. You need to remember, that sometimes even if the narcissist cannot get a new partner, you can clearly see his/her search for the narcissistic supply from other sources like extreme focus on career, learning philosophy etc
3. Discard you all of a sudden when he/she feels so:
This is the saddest thing, and also the biggest truth about a narcissist. When the narcissist is ending the relation, he/she does it in a sudden awkward way. They can suddenly block you and discard you even without any reason. In fact, this is what makes a breakup with the narcissist a nightmare.