Emmuss's Favorite

I mean, there are different types of affection.
If he views that bird as his emotional support animal, to whom he can confide himself to, he would naturally end up feeling affection for it and might get possessive over that established master-pet bond. Affection doesn't need to be romantic.
That and they are in a warzone. So being possessive and jealous of others who could potentially take away that little ray of sunshine, who allows him to relax and express himself freely, is expected. She isn't a soldier. She is a bird.
A very bright bird that interacts with him willingly. She is there with him because she wants to! A bird who could fly away and never return since she is chained by no human-constructed social, moral, or ethical obligations!
He is the chosen one. The chosen master of this genius of a bird.
It will undoubtedly make him feel special and loved. And although I've never been on a battlefield, I think I would crave for these little moments where my rank and mission weren't of any importance for me to feel needed and appreciated.