At the Filipino ReaderCon panel I was part of, I shared my "secret" to writing romances: I happen to believe, based on reading a gazillion Sweet Dreams novels, that there are only three types of love interests in this category. The Unattainable Crush, The Best Friend and The Jerk.
I wasn't able to explain in detail then, so here it is now. These three guys are actually not so much guys, but templates for a relationship dynamic. How does the main character (MC) relate to this love interest?
The Unattainable Crush (Lucas, Dante, Anton, Quin)
Also known as The Jock, The Popular Guy, The Alpha Male, The BMOC. It doesn't matter what he does or who he is, I've learned; what matters is how MC reacts to him.
She thinks he: is out of her league, is crazy for being interested in her, probably has girls lined up to be with him.
He thinks she: is underestimating herself.
He: doesn't believe in his own hype.
The Best Friend (Zack, Robbie)
Must be a guy who is more special than other friends. The other guy friends may be interchangeable, but this guy is not.
She: trusts him.
His main concern is: the fact that he is friendzoned, and for who knows how long.
The Jerk (Manolo, Diego)
This is a difficult relationship to write because there's a line that shouldn't be crossed, ie he can't be a real jerk or else the journey isn't worth it. Usually he has his own reasons for being an ass, but they're never that bad.
She: actually enjoys sparring with him.
He: is challenged by her.
My husband doesn't believe this just yet, and has some objections.
It's impossible that there are only three types! What about The Stranger?
OK, fine. So when I write the scenes with the main character and The Stranger, what is their relationship? Is it awestruck attraction? Is it friendly? Is it adversarial? (See three templates above.)
But Villains are Jerks too!
MC has a relationship with the villains too, and any of those guys could be a villain in an MC's story. I've had fun with making villains out of friends.
The short answer always is, it all depends on how MC reacts to him. That is what turns a guy into a love interest, a spurned suitor, an evil ex.
When I was first published, my first little goal was to write 3 books, one highlighting each love interest type. Of course by now I've written more, so my new challenge (with Interim Goddess of Love) is putting all three in one story and making each one worth choosing. So hard, since I love Quin, Diego and Robbie pretty much equally by now, but it's really going to be about who the MC Hannah will choose. And she will choose somebody. (I'm going to make her!)
There's a risk with building characters this way -- not all readers will want to join a certain guy's team. People who love best-friend romances might not agree with ever hooking up with a player. People who like confident alpha types may think kissing a friend is gross.
Readers are MCs too.
At the Goodreads TFG anniversary, Ariel asked me how it felt to have people come up to me and tell me they liked one of my books. I told him (something to the effect of) that I loved it, because it reveals something to me about the reader. Who's your kind of guy? Did the story help fulfill a wish, reinforce what you know to be true, or sway you into accepting a new type?
So this is my "secret." Yes, I think about these things. I hope this is useful for you too.