Welcome to our forum.
If you poke around, you will see that there are many helpful threads here. Plus you can always post when you have a thought, question, or concern.
My experience has been that sometimes the first few years (in a poly relationship) are hard to navigate, but it gets easier and you do figure out what works for you. I think a lot depends on how closely involved you are with this other couple.
Let us know how we can be supportive and helpful.
Love means never having to say, "Put down that meat cleaver!"