Struggling with the Emotion of Discarding a Healthy embryo

Hi - My Wife (43-year-old F) and I (42Y old M) had my son 4 years back through IVF. He is the sweetest child, active, rambunctious, and all that a 4-year-old should be. He is also on the spectrum, which means we spend a ton on therapies, etc, to ensure he gets the help he needs before he transitions to mainstream school. We have another embryo on Ice at the facility, and after 3 years of discussion and mental preparation (mostly for my wife), we decided to discard the embryo. As we sign the papers today, a tremendous guilt is swooping over us, if we are doing the right thing.
On the practical side, I know my son needs a lot of help, so our resources are dedicated to him. We are also aging, so it doesn't make much sense to have another kid at 45. But on the moral and emotional side, we are both split.
Has anyone gone through these motions? I knew in my heart I wanted one kid, but why does it feel wrong, even though I know the decision is for the best of my family?