The ROs are all monogamous, so no polyamory there.
There will be some scenes of jealousy in the future that I have planned, both coming from the MC or the ROs depending on the route you're reading. But it will be a very minor thing and will not change the dynamic nor the romance.
And about the love triangle routes, I did think about doing at least one (more specifically Leire/Luca with Rayco/Gara) but I quickly discarded the idea because of how much work it would take. I'd have to create a whole new route just for that, add even more variations, choose scenes between them and how the other feels about it, the different endings, etc. It's just too much for my first game. There's already enough drama in the story and in each route to add even more lol. I rather focus on each of them individually and let the players experience the romances to the fullest without a third person in the mix.