Part 1 of Fictional Science or Scientific Fiction is:
One "fictional science" that a writer can use to generate Science Fiction Romance is psychology. It intersects with religion and culture.
If you are building an Alien for your Main Character to fall in love with, you need to consider the core questions "What Does She See In Him" (and vice versa).
The answer to that question is equal to the reason the reader would be interested in this novel -- that is, the answer to "What Does She See In Him?" is THE THEME of your novel -- subset under the master theme of the genre, "Love Conquers All."
All genres have a master theme, but the best editors sort novels into genres not by what they contain, but rather by what they do not contain. People often read fiction to avoid thinking about something -- love being one of the somethings.
But Science Fiction readers tend to choose novels to read by what they do contain -- Aliens, Strange Cultures, and above all, ideas about what errors there might be in our current solemnly believed science.
So what errors might there be in our definition of "human?"
We currently study "human" as a variety of Great Ape, and science is probing brain structure and brain activity to attempt to account for all human experiences, especially experience of God, the Soul, Life after Death, and even the sense of "self."
What if that approach (NOTE THE "WHAT IF...") turns out to be counter-productive once we meet up with Aliens who have a civilization, interstellar travel, but despite physical differences, have Souls that Mate with human Souls?
The "Science" ingredient in such a Science Fiction Romance would be what we currently call "Anthropology" - which science fiction traditionally expands to become "xenology" or the study of aliens.
What if your Aliens typically have memories that extend back before birth (or hatching, or something else). What if their entire culture is based on those long-memories?
What if they can't deal with humans because we don't have such memories?
What if they are telepathic and determine that humans do have such memories but refuse to acknowledge them?
Whole cultures and vast matrixes of belief systems (some conflicting with others based on the same text) are often derived from Parables.
A Parable is a "show don't tell" of serious drama stripped down to bare essentials to reveal an underlying "truth" that appears across many cultural barriers.
Here is a Parable that came to me anonymously via a WhatsApp contact who got it from someone who didn't know where it came from. A meme.
In a mother’s womb were two babies. One asked the other:
“Do you believe in life after delivery?”
The other replied, “Why, of course. There has to be something after delivery. Maybe we are here to prepare ourselves for what we will be later.”
“Nonsense” said the first. “There is no life after delivery. What kind of life would that be?”
The second said, “I don’t know, but there will be more light than here. Maybe we will walk with our legs and eat from our mouths. Maybe we will have other senses that we can’t understand now.”
The first replied, “That is absurd. Walking is impossible. And eating with our mouths? Ridiculous! The umbilical cord supplies nutrition and everything we need. But the umbilical cord is so short. Life after delivery is to be logically excluded.”
The second insisted, “Well I think there is something and maybe it’s different than it is here. Maybe we won’t need this physical cord anymore.”
The first replied, “ Nonsense. And moreover if there is life, then why has no one has ever come back from there? Delivery is the end of life, and in the after-delivery there is nothing but darkness and silence and oblivion. It takes us nowhere.”
“Well, I don’t know,” said the second, “but certainly we will meet Mother and she will take care of us.”
The first replied “Mother? You actually believe in Mother? That’s laughable. If Mother exists then where is She now?”
The second said, “ She is all around us. We are surrounded by her. We are of Her. It is in Her that we live. Without Her this world would not and could not exist.”
Said the first: “Well I don’t see Her, so it is only logical that She doesn’t exist.”
To which the second replied, “Sometimes, when you’re in silence and you focus and you really listen, you can perceive Her presence, and you can hear Her loving voice, calling down from above.”
The "science" fictionalized here is what we call Religion - or the belief system that includes Soul.
Your writing exercise is to fictionalize some science you know something about and write the Parable most often quoted by your Alien Hunk's primary culture as the reason or motive behind their behavior -- as we point to Soul Mates as the reason for Love At First Sight.
Then write the dialogue where he/she explains the meaning of the Alien parable to a human (pick an Earth culture for your human).
See what they think of each other after that conversation.