Villain/enemy:
Hotelier ML#2 was an expert recruited by the business and love rival of the late hotel owner to takeover the hotel, but he fall in love at the first sight of FL yelling at a waiter in Las Vegas.
If I Can Love You So SML was the older brother of FL's late cheater husband, trying to sabotage ML and FL's relationship but end up falling for FL.
Lost You Forever ML #3 was the general of the remaining people from the third kingdom that's long been disappeared/lost (300 years?), at first he used FL as he needs her bloods but end up falling in love with her. Had S2
Prince of Lan Ling I actually forgot if SML was obsessed or really in love with FL, but he's the enemy from a stronger country. Ending spoiler: Different from the history, ML was alive and well but FL died living behind a daughter maybe?
Queen of Tears SML, who's trying to rob FL's mall, property and money, was obsessed with FL since childhood
The Heirs SML was a typical bad boy, with trauma after being left by his mother
SML strongly dislike ML:
Fated to Love You (iirc) SML dislike ML for standing on the two boats, hurting FL, hurting his real younger sister, yet shamelessly want FL back.
Flourished Peony ^v^ has an upcoming sequel SML was FL platonic husband, dislike ML's unusual behaviour, teasing, thick face, being 'greedy' official and more, but especially so because he's 'living together' with FL.
Hi My Sweetheart SML dislike ML for flaunting money and power, being playboy, having the same face as FL's 'first love' and seducing FL.
Rival:
My MVP Valentine SML and ML were basketball team members from different schools that's on the top two in their region.
Queen Seon Deok ML #1 and ML #2 were best friends and rivals in military and love, but in the end ML#2 becomes villain.