Good vows aren't invented, they're remembered. The job right now is not to write well. It's to collect specifics: moments, habits, small ordinary things nobody else would know to mention.
Set a timer for fifteen minutes and answer whatever comes. Fragments are fine. Half-sentences are fine. If a prompt does nothing for you, skip it — there are more than you need on purpose.
One rule as you go: prefer the small detail over the big statement. "They love me" is a statement. "They text me the weather before I leave the house" is a vow.
When you're done, read it back and put a star next to anything that makes your chest go tight. Those starred lines are the ones we'll use.