The most authoritative reference I can find is in this interview with Collins's editor Kate Egan:
What are Suzanne Collins’s strengths and weaknesses as a writer, and how do you help her as an editor?
Storytelling is Suzanne’s strength. As an editor, I help her develop the characters. For example, I asked her for more of the Peeta-Katniss-Gale love triangle. Suzanne was more focused on the war story. We’ve learned to trust each other. Sometimes Suzanne thinks it’s obvious where she is going, but I tell her I don’t see it. When I need help following, it’s a sign that the manuscript needs some shoring up.
Which suggests the love triangle was there originally, but the author wanted to put less focus on it.
Collins herself is notoriously reclusive, and has given very few interviews relating to the Hunger Games, none of which seem to mention this issue, so it looks like this is the best we're going to get.