"Sitting by Mark’s side for these 14 years has been the honor and privilege of a lifetime. [...] In the critical moments of my life, in the highest highs and in the depths of true lows, I have never had to turn to Mark, because he was already there." If this is an accurate reflection of her experience, I don't expect it's a side of Mark Zuckerberg most of us imagine exists.
I've not read anything (else?) Mrs Sandberg has (or hasn't) written, but this turn of phrase has a "professional" feel & taste. It's contrived. It's not something you would say about someone truly dear to you, your best friend, your parents, etc.
Maybe your dog.