Fears and expectations that date back to earlier experiences of dependency, but that didn't arise during courtship or dating, are activated as commitment to the relationship increases. As a result, partners start to anticipate the worst, not the best from their relationship.
Stan Tatkin, Wired for Love: How Understanding Your Partner's Brain and Attachment Style Can Help You Defuse Conflict and Build a Secure Relationship
commitment, dating, fear, love, relationship