'Sweet' = light tone, smooth romance, almost no separation. 'Angst' = repeated separation, misunderstandings, sacrifice, usually ending BE or Bittersweet. We classify using three axes: ending type, trigger intensity, and who-it's-for.
Quick rule: HE + low-intensity warnings = sweet. BE / Bittersweet + multiple high-intensity warnings = angst. Anything in between is typically sweet-then-angst or angst-then-sweet — check the mild-spoiler layer.