Meaning of "the soul holds its own anniversaries and all that"?

Hello everyone. I am reading a novel, and I came across this expression. Could you please let me know its meaning?

This had been one of the worst days of my life. The worst, actually. It would take a few days, maybe another week, then I’d put the whole thing behind me. Or was I underestimating the damage? Give it a year, until next Christmas Eve—the soul holds its own anniversaries and all that . . .

- André Aciman, Eight White Nights, Sixth Night

This is a novel published in the United States of America in 2010. This novel is narrated by the nameless male protagonist who meets Clara at a Christmas party in Manhattan. The protagonist goes to a bar with Clara and meets her friend Victor. But he soon goes home, leaving the two behind at the bar, because he feels that he is the one-too-many in that group.

In this part, I wonder what the underlined expression means.

I especially wonder what "holds" here might mean; would that mean that a human's mind maintains/keeps its own special dates in which special events happened...? (Though this is just my guess. )

Thank you very much for your help.