You Won’t Kill Me This Time, Crown Prince!
My prediction is that this is similar to “Father, I Don’t Want This Marriage”, where there is a lot of things going on in the background that the FL is not aware of. Except in this case, instead of the FL killing herself, the ML does to trigger a restart, because he screwed up in not telling her what was going on (though he did try to hint at it by saying “wait for me”). I’m not going to label the leads as “shitty” or “dumb” yet, because while the FL was ignorant and naive in the beginning (a typical story trope), I will wait to see if she continues to be as the story progresses. As for the ML, I don’t think he betrayed her, he was just stupid in thinking he could solve the problem on his own, without clueing her in (before he left for the war).
I am the Master in this Life