Why did christian want roxanne to choose between cyrano and himself?

Cyrano asks Christian why he is so pale and upset, and Christian confesses that Roxane does not love him, but loves Cyrano. Cyrano disputes this and tries to comfort him. Christian plans to tell her the truth and perhaps the marriage could be annulled -she must love him for himself. He also realizes that Cyrano loves her, and encourages him to tell her.