I really hope there is a bitter end to the relationship of these two. I don’t think I would be satisfied with him just switching sides. As a lifelong Gundam fan, I feel her betraying him could really help remind readers that wars are more complicated than good side vs bad side.
Unfortunately, I have read enough Korean webcomics to know that the most likely end is him switching sides and being strung along as the secondary ML for the remainder of the series. I do feel this one could be different though.
Dammit, writing this comment has reminded me of 0080 and now I am depressed despite not seeing it for over a decade.