Hwayugi / A Korean Odyssey - the other guy isn't in every episode; the SML (who has a love/hate bromance with the ML but supports him when things get serious) has his own romantic interest and is never romantically interested in the FL
Because This is My First Life - two guys other than the ML pursue the FL at different points in the story, but neither has a big enough role to be called the SML; if there is a SML it's probably Sang Goo - the ML's boss / friend and the love interest of one of the FL's friends
Bromance - Qing Yang is the SML (he's the ML's relative + closest friend and has his own love interest) not Zhe Rui (the other guy in the triangle)
Fight For My Way - the FL's ex has a small role in the story; the SML and SFL are dating and they + the leads are best friends
And maybe:
Love in the Moonlight - I'd argue that Byung Yeon is the SML; he's the ML's bodyguard and closest friend; he cares about the FL but doesn't have romantic feelings for her; he doesn't have his own love interest; the other guy in the love triangle is Yoon Sung
Love O2O - the ML has three good friends that sort of collectively fill the SML role; one of them has an implied love interest; none of them have romantic feelings for the FL; the other guy who likes the FL is Cao Guang
Moon Lovers: Scarlet Heart Ryeo - I like to think that Baek Ah is the SML; he's the ML's relative and closest friend; there's more than one other male character that has feelings for the FL (it's a reverse harem set up) but Baek Ah is just friends with the FL and has his own romantic storylines
Something About 1 Percent - there isn't really a SML, but the ML's cousin might qualify; he's originally considered the ML's rival but becomes his ally; he never has romantic feelings for the FL; the other guy in the love triangle is the FL's friend's brother; his role is pretty small
Witch's Romance - I think the ML's best friend Soo Cheol has at least as big a role as the FL's other romantic interest; he lives with the ML and they start an errand business together; I can't remember if he has his own love interest but he never has romantic feelings for the FL
