Certified GKH Gardening Expert
I'm not certain what you mean. Are you trying to grow spinach with butternut squash? The squash dying will not have anything to do with spinach growth.
Is this Petersfield, South Carolina? The heat, coupled with rain that much of the US has had recently can cause infections that may kill off plants.
Unfortunately, I don't have enough information to give you a good diagnosis at this time. In the meantime, this article will help you to grow Butternut Squash: https://www.gardeningknowhow.com/edible/vegetables/squash/growing-butternut-squash.htm