Lost twin

I had my daughter November 2019 and we were pregnant with twins and sadly her twin didn’t make it through the pregnancy.

Has anyone ever wondered if the surviving twin is ever affected by this?

I can’t help but wonder what our lives would have been like had she survived.

Also I don’t know if I should tell her she is a twin from early on or wait until she’s old enough to fully comprehend? I know I’m incredibly lucky to have her and I’m so grateful and love her immeasurably, I just watch her playing sometimes and the pain strikes.

Am I selfish for being sad when I have a healthy baby? I sometimes feel like I shouldn’t be mourning the loss of my baby because we are a lucky to have her sister.