The chain of idealistic devotion -- Decoud loving Antonia who loves her father -- has been broken, despite everyone's intention of keeping it together, and the Separatism that Decoud set in motion in order to stay with Antonia, has ended by separating him from Antonia, as it must.
We may summarize the plot of this romantic tragedy as follows: Antonia wouldn't leave Don Jose's side to flee the country, but Decoud couldn't stay (the Monteros would have killed him), so he invented his plan of Sulaco Separation in order to preserve his safety and remain in the protected Sulaco with Antonia. But the revolt of the parliamentarians, who are planning to welcome Montero, has wrecked their plans. Decoud can no longer be with Antonia -- he can only escape or die. Worse, Separation can only be accomplished behind the parliamentarians' back, forcing Don Jose into a position where to agree with it is unpatriotic, thus sacrificing his ideals and causing his spiritual death, which in turn causes Antonia's. She averts her face from Decoud and pulls her hands away, signifying even more strongly that her primary allegiance is still to her father.
Note that Decoud's initial ambition was a compromise between separatism (of
Sulaco) and union (with Antonia), and that it has been destroyed precisely by
the masters of compromise: the parliamentarians.