My comment's late and I'm not gonna bother to @ing at previous commenters, but here's my take on it that should clear things up for future readers.
Tini's goal is to find the perfect man/leader to stay in the unit and help lead the soldiers, so obviously once MC announces he will leave after a year, already ruined her plan.
She also isn't a "easy girl"(probably still a virgin), she took so long to even make moves on the MC, and she most likely was the first to stop the seduction too. She plays it smart, not throwing herself away at any man.
And MC's just got other places he needs to be cause of the plot. Maybe Tini will appear in the future, who knows.