It's not that Historia saved herself from being fed Zeke but Eren's own opposition to the pregnancy plan. He did not want Historia (or any Eldian) being made into a breeding cow to pump out progenies to keep the Titan inheritance going (throwback to initial chapters where Eren hated the reality that Eldians are like livestock confined within walls forced to breed and enjoy false peace).

As per you, Eren getting frustrated that Historia mated with someone else is a gross indicator of Eren's love for her. AOTnR team had mentioned they are not going for any particular ship route. Eren likes Historia, but him Rumbling the world for that reason is as pathetic as the 139 'No I dont want that panel".

As for why it has to be Eren to be the father, Historia mentions that if she has to get pregnant, she atleast should have the choice of who should be the father. Aside Ymir(dead), only Eren was that close to her. Eren lashing out at Armin's exposure to the secret is another indicator he did not plan himself to be the father and wanted the child's father identity to be secret