there's a man's secret medicine scattered around that grows whichever dude drinks it by 1 cm. I think there's enough to get to 19. (there's also woman's secret medicine that increments bust size by 1)
As with basically all of this devs games, MC basically only has sex once married. Which is like, 3/4 through the game or something ridiculously long like that. No. Holy affinity doesn't block you. (I have yet to find anything affinity's do except maybe impact willingness to room with each other?) MC just has a lot of strong opinions about when it's okay to have sex and the thots throwing themselves at him need to calm down until married or find another dick.
So in summary: depending on your definition of loser, Theo never really changes. No sex until marriage. But you can magically grow your dick bigger with medicine (and it impacts the ladies satisfaction)