This is why, when I dipped my toe into poly for the first time with my best female friend, I didn’t do anything sexual until a long time had passed, first were many discussions with my partner, with her partner, I spent time with her partner as a friend so he could feel safe, we set out the understanding of what the expectations were and that we valued our friendship first so if either of us had to step back or slow down from the sexual stuff because our partners needed time or changed their minds we would be OK with that, and communicate it, and we would always be friends either way. There have been some interesting conversations but so far it’s progressing well. Whatever communication is needed in a monogamous relationship is quadruply needed in a poly relationship.