Glad you're here.
Even though the geometry of your polycule is relatively unusual (three-person set-ups are more common), many of the principles remain the same. They sometimes say, "First year forming, second year storming, third year norming." That's highly generalized in real life, but the point is you should expect a certain time of "storming" after the "honeymoon phase" is over. Then, don't panic, as a norming phase will in time occur.
That said, I admit that quads sometimes have a hard time holding that configuration, and not dissolving into a trio of some kind. However, you should think in terms of what applies to *you*. Every person is different, and every relationship is different, too.
Love means never having to say, "Put down that meat cleaver!"