First of all: Welcome! c:
Each playthrough is a character all on its own, meaning that your other characters will not be affected.
As for the Love Triangle route itself, well… It is the route with the most angst in it, so there will be feelings that get hurt, yes. And there will always have to be choices made in regards of favouring one above the other in certain scenes. Though I can be wrong in this regard, since I have not played that route yet! But this is what I have come to understand about it after reading quite a lot of comments about it.
Possibly? It is all part of the angst. Though I personally think there will not be too much (if at all) jealousy between the two, since N and A have an incredibly strong bond and have lived who knows how long with one another. They have grown attached to one another and only want the best for each other.
Seraphinite , the writer, is working on setting up a Patreon. So there will definitely be announcements about them on the threads and her personal media. Keep an eye out for it c; (her Tumblr and her Instagram)
Hope this helped. If you have more questions you could always check the second comment on the other Wayhaven thread where you can find the FAQ.