Ember's fate was in his hands.
If he chose to ignore this, Ember would never be born. She would never exist.
He had a chance to decide. He had a choice to make.
If he did this dark magic spell and made Ember's existence possible, he would subject her to everything she had ever witnessed, expose her to the clutches of Lydia, and revive her fate as a witch.
However, if he chose not to participate in the dark magic spell, there would never be an Ember in his life. Every trace of her on earth would be wiped off.
Which of these fates should he chose? Which of these fates seemed right to chose?
Lydia certainly wanted him to go for the one he would want to protect Ember. The one that would make Ember's existence impossible.
That was presumably why she had brought him back to this exact moment.
She wanted him to make the choice. She wanted him to decide Ember's fate and hopefully, erase Ember's existence.
