I wanted to share my experience of growing up with a brother, but now being an only child.
My brother was 3 years older than me. Growing up, we rarely played together. He had his friends and I had mine. When we did intereact, we usually bickered constantly (I don't know how my parents handled us). Honestly, I think having a sibling growing up added a lot more tension to our family. The kids fought, money was tight, both parents worked, and stress levels were constantly high.
My brother passed away 4 years ago, when I was 23 and prior to having DS. Of course I was upset at losing my only brother, but it really did not impact my adult life. We already lived in different states. We were nice when we saw each other, but we never went out of our way to call/email the other.
I'm sad that DS will never get to know his uncle, but we have a ton of great friends that are called "Uncle" for DS. I don't feel like there is a huge absence in my life because I'm an only child. My brother and I would have always lived in different states. I have fantastic girlfriends that serve the role of "sister" for me.
My parents divorced when I was 17. The hardest point about being an only child is being an only child to divorced parents. It feels like 2x the obligation because there are 2x the visits, 2x the phone calls, etc.
Bottom line is that after experiencing both options, I will not feel guilty for raising DS as an only child.