It’s most obvious in ANH with Luke and Leia’s reactions. In fact I think within the context of that film, Luke and Leia are meant to get together. Han acts more like a mature big brother who plays “cool” with Leia.
Best evidence here is that scene after escaping the Death Star where Luke asked Han about Leia, and Han says no chance, this is clearly aimed at a bit of love triangle. A naive, caring guy vs your typical detached, cool guy. Clearly setting up.
But something must of happened between ANH and ESB, because Empire doesn’t really seem interested in playing up a love triangle. Leia kisses Luke in that instance to make Han jealous. The entire B plot of that movie is dedicated to their relationship, so it’d be weird for Luke to just show up again. But in the same token they’ve already set up a love triangle.
Had ROTJ stuck to its guns with the original script, either Han’s death or Luke walking away to focus on the Jedi would have made a far stronger conclusion to the triangle.
I don’t think Han asking about his chances with Leia was necessarily setting up a triangle. He noticed Luke was interested and decided to mess with him. Otherwise, I’ll defer to my last post in this thread.
When SW was written, the intention was that Luke and Leia would ultimately end up together (simply because that’s how these kinds of stories usually work). She’s immediately dismissive of both of Luke and Han, but quickly comes to respect Luke while the same cannot be said for Han. Except, Leia happened to have more chemistry with Han.
When they wrote ESB, they clearly noticed this, so they decided to add the Han/Leia romance with a strong love triangle in mind. This was prominent in early drafts and deleted scenes. When it finally came down to it, and the film was trimmed to what it is with extraneous bits removed, we ultimately have a movie where Luke expresses no romantic interest in Leia and vice versa, only one scene where Leia kisses Luke to make Han jealous (with any other romantic context for their kiss completely left out on the cutting room floor).
So in the end, yes, the love triangle never manifested. SW very lightly suggests that Luke and Leia might be a thing, but in the context of the next two films, it is much easier to ignore this and focus on Leia and Han’s bickering, which while not romantic in the original became such in ESB (which retroactively make them seem so in the first film).