Please help me understand this passage

[YOSHITAKEHORI]

I cannot understand the underlines sentence. And what does
"it's depth" mean? Could anyone help me?
qot
I just looked at my friend with disbelief as he told the story of the first day we met. He had planned to kill himself over the weekend. He talked of how he had cleaned out his locker so that his Mom wouldn't have to do it later and was carrying his stuff home. He looked hard at me and gave me a little smile. "Thankfully, I was saved. My friend saved me from doing the unspeakable." I heard the gasp go through the crowd as this handsome, popular boy told us all about his weakest moment. I saw his Mom and dad looking at me and smiling that same grateful smile. Not until that moment did I realize it's depth.
Never underestimate the power of your actions. With one small gesture you can change a person's life. For better or for worse.
unqot

[Tdol]

It should be 'its depth' and it refers to the smile, which is a more profound smile than the narrator had realised.

[YOSHITAKEHORI]

Tdol
Thank you very much. Can I undestand that meanig as " I realized its depth for the first time at that moment." ?