Huh, I looked hard and still don’t get how this is unclear. The “their” isn’t me because it’s third person, and it can’t be the region of South-East Asia or high school guy himself because that doesn’t make sense. That should leave one possibility. Singular their is a thing, if you’re unfamiliar.
I’ll just clarify. My South-East Asian cousin married someone not in the story, and their college roommate, high school guy, was present as a guest, which was highly unexpected. Hilarity ensues.