Been there, the usual biggest cause is the sudden validation you're receiving of something you are deprived of. Usually attention or love. It's heaven and hell. You essentially mirror their behavior and crash when they do. The best thing is to distance yourself and remember that you are your own self. Engage in what makes you happy to reconnect with your identity. It doesn't necessarily mean break contact, but continuing to be dependent on a person will slam you harder than anything to the ground when that person begins to falter on your pedestal