Soldato
Eugene is a weak survivor. He's loyal to whoever is keeping him alive in that particular moment. He'll stick with Negan for now until something happens to change that. The question will then be how Rick's lot see that. If they view it as him betraying them then he could be in trouble.
In fairness it's what makes the show so watchable. There isn't a character that isn't flawed in someway, it gives the writers opportunities to take the story in different directions at the drop of a hat. We haven't seen or heard much about his back story as some of the other characters, so I wonder if that will unfold a little more as he makes his choice. Definitely a better episode this week.