"Romance is between people who aren't directly blood related- Who aren't children or parents to each other. If they're directly related it's almost always indulgent type feelings and it's just called a parent-child relationship... There's basically three kinds of romance. We call them lifepartner, fascination, and indulgent romance. It can be more than one, or none of these, but most people find it useful to use those words to describe how they feel.
Lifepartner romance is with someone you think makes you a better person, or someone who you like being around because you admire them and want to help them, or someone you feel a personal connection and loyalty to, whose life-routines mesh with yours well. It's a quiet, calm, and... Intellectually happy, I guess, feeling?
Fascination romance is with someone who you find interesting, compelling, someone who makes you emotional and adventurous, who you want to prove yourself to or find thrills together with, or who you want to entice, flirt with, and seduce. It's an intense and thrilling feeling, like winning a closely matched game. Some fascination romances look like friendships and some look like rivalries. I have a fascination romance with one of my classmates who writes fanfiction in the same sites as me- I almost hate her but I'd be really sad if we never talked to other again because the rivalry is so compelling! That's textbook rival-type fascination romance, honestly!
Um. Indulgent romance is with someone who makes you feel loved and comforted, who you think is beautiful or accomplished or amazing. Someone who being near feels warm and pleasant just because. Someone who you want to make smile and laugh and happy and comfy. It's a sweet, sappy, and sentimental feeling.
Sex comes paired with all three romance types often but not always, and also sex happens a lot outside of what you'd call a 'romance' but it's- It feels different, it's less... Meaningful and heavy? It's not important. It's just stress relief or passing time if you're not pursuing romantic feelings. Except you need to be on birth control pills most of the time and avoid sex with close relatives, uh, the elders keep track of that and give you a list of people to not fuck."