Genuine alien psychology, not human in disguise
The fundamental challenge of alien romance is creating a character who is genuinely different in their inner life rather than merely different in their appearance or culture. Genuine psychological difference means different structures of perception, emotion, memory, and desire — not exotic versions of human psychology but different operating systems entirely. The alien who experiences emotion as color rather than feeling. The alien who forms attachment through shared silence rather than shared speech. The alien who has no concept of romantic exclusivity because their species forms bonds that are not possessive. Each of these differences, followed consistently through the character's behavior and decisions, produces a character who requires real work to know and whose eventual closeness with the human protagonist feels like a genuine achievement rather than an inevitable narrative destination.