First, name the feeling before presenting the analysis. "I felt sidelined when the milestone got postponed" is more useful than a careful case for why the original date should have held. Second, after any difficult exchange, write down the trigger, what you told yourself it meant, what you felt in your body, what you did, and what actually happened. Over time, that record reveals which interpretations were accurate and which were anxiety filling in blanks. Third, make one specific request instead of several open-ended ones. "Can we reschedule by Thursday and confirm a new date?" is actionable. "I just need to know you're still invested" puts your partner in an impossible position and rarely produces the reassurance you are actually looking for.