@SnowdropGirl15 Hi there! I have several tips on how to write a good love triangle story:
1.) Make each character (A, B, C) compelling characters in their own right. Specifically, give B (the center of the love triangle and is almost always female) a personality and active role in the story, not a reactant or plot puppet. Likewise, make sure that the entire narrative surrounding A and C (the contenders for B's love) does NOT revolve around B. They each have their own thoughts, feelings, motivations, etc. outside of B.
2.) We, the audience, need to understand why B could decide either way - why A and C are both contenders in their own right. B needs to have chemistry with both A and C, but a different kind with each of them that each work. Thus, B needs to spend time with both A and C, developing different relationships with both characters that each work equally well.
2.) Don't make it obvious which side will "win" by having B clearly favor one side before they officially choose. The entire point of a love triangle is wondering if B is going to choose A or C. The audience will only get frustrated if it seems like B already made up their up and is just hemming and hawing for no reason other than "drama."
3.) Pace the story properly. Make sure that the love triangle doesn't get resolved too quickly or dragged out for too long. There should be a certain ebb and flow in the story, which keep the readers on their toes and lead to proper conclusion.
4.) Let the triangle run its course. Keep in mind that there are only so many times B can sit down and wonder who to choose before it starts frustrating. And that B's indecision will make the readers why A or C haven't moved on. So, don't be afraid to have B wind up with A or C before the end of the story.
Thank you for reaching out. I hope that this helps you.