Enlightened Confidant

If a card in your graveyard has an X in its mana cost, X is 0 for the purpose of determining its mana value.

Enlightened Confidant's ability checks at the moment it would trigger to see if you gained life this turn. If you didn't, the ability won't trigger at all. Once your end step begins, it's too late to gain life in order to cause this ability to trigger. However, the last part of the ability will check how much life you've gained as the ability resolves, so you could still gain more life while the ability is on the stack to make putting a card into your hand easier.