why DO i feel the need for constant reassurance from my partner?

Reassurance seeking behavior is very commonly seen in individuals who have an anxious attachment pattern. The desire to seek reassurance is a self-soothing mechanism that can help the anxious person to feel more at ease within the relationship as they are more likely to struggle with fears of their partner rejecting or abandoning them. 

From an attachment perspective, someone with an anxious attachment style most likely grew up in an environment where their primary caregivers were inconsistent with meeting their emotional needs resulting in a lack of safety/trust and is why they developed these reassurance seeking behaviors. 

While seeking reassurance at times is a normal part of even healthy relationships, constant reassurance seeking can create tension and further divide in the relationship. This is more likely to be increased if the anxious person is quick to assume that a shift in their partners mood/behavior is related to negative feelings towards them and are unable to self-soothe these anxious thoughts and feelings. 

The first recommendation for those who struggle with reassurance seeking is gaining awareness into your desire to seek reassurance, identifying what your triggers are and where this stems from. It is also important to communicate your needs with your partner in an open and honest way when seeking reassurance rather than resorting to mental games or tactics. Lastly, mindfulness based skills can help those with an anxious attachment style learn how to self-soothe when they are feeling activated and practice self-assurance vs. constantly turning towards others for reassurance.