This trope is hard to find. Everywhere is someone, who is more or less involved (at least has a crush).
I'm Not a Robot - there are 2 exes, but both are insignificant in romance story of the leads. So I would say, that those can't be considered as love triangles.
I don't watch kdramas much, so there aren't other kdramas, that I could recommend. Maybe you could try other land dramas. For example these 2 cdramas are sweet:
My Little Happiness - love triangle for only few episodes in second leads' story, main leads has beautiful romance.
Sweet Teeth - no triangles, multiple couples, sweet story
