I don't believe there was any type of love between Gestahl and Terra except the whole somewhat parentage since Terra was taken from her family when she was just a baby. Gestahl probably took care of her and raised her until he needed her to do what he wanted her to become, a Magitek Warrior.

Gesthal found Terra when he entered the esper world and started capturing the espers. The esper elder decided to cast a strong spell that would prevent the humans from entering and the espers from ever entering the human world. It was during this time that Madeline made the decision that she could not be seperated from the human world even if she did care about Maduin and the baby. Without a word to Maduin and while the spell is being cast, Madeline takes the baby with her and runs to the entrance.

By the time Maduin heres about it and makes it to Madeline side, it is very close for both to return. Madeline agrees that she has enough strength to return back with Maduin and the baby to the esper world, but the strength of the spell causes them all including the baby to be trapped outside the gate in the human world.

This is when Gesthal finds Terra. Maduin is down along with Madeline. Gesthal spots the baby and makes a connection that baby is half esper and half human. He thinks that the idea is fansinating and tries to take the baby. Madeline spots this and tries to take her baby back, but Gesthal knocks her down, ending her life, while Maduin is taken back with the rest of the capture espers.

The Gestahlian Empire