Fear of the unknown is the key. 

Remember, no relationship is 100% secure. Relationships are about the future,  and the future is an unknown.  That’s why trust is so important.

Fear can cause the need for high levels of intimacy, needing approval and responsiveness from partners, making you overly dependent on your partner.

This can cause you to be less trusting, have less positive views about yourself and your partner, and may lead to high levels of emotional stress, worry and impulsiveness in your relationship.

Securely attached adults tend to have positive views of themselves, their partners and their relationships. They feel comfortable with intimacy and independence, balancing the two.