External conflict on its own rarely stands up as being big enough, emotional enough or important enough. Yes, external factors are important in keeping a story moving, but internal factors are the driving force behind character arc and development, and our pathways to making two-dimensional, imaginary characters human. Real.
But the one thing that a book must have to count as a romance novel at all is either a Happily Ever After or Happily For Now. The reader goes into the story knowing that everything is going to turn out all right in the end, better than all right, no matter how dire the circumstances may seem.