Well, here is the thing. When we write romance in fiction -- just throw your own experience with romance in reality out the window, mostly.
People don't want to hear so much about the regular romance of everyday people ("We went to see a movie then snogged for a while"). People want extraordinary romance! It's the same principle about main characters, most people aren't interested in a main character that is so regular that they're indistinguishable from ordinary people.
There are no real novels entitled "My Job At Chilis and How I Don't Like It." They want an extraordinary character that still has parts that they can identify with somehow. This is why it is such a popular trope in contemporary novels to have an MC start out being a nobody and then discover his or her extraordinary side.
That said, how to write believable extraordinary romance? Well, that's where I have less of an answer for you. I've read bodice ripper novels all my life and I am still not great at writing romances so I generally don't put heavy emphasis on it in any story I write.
Read a lot of romance novels/stories.
There is a Chinese saying, "If you read ten thousand books you'll write like a god." So that is my advice.