What does the song "First of May" mean?

Question

This is the lyrics:

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When I was small, and christmas trees were tall,
We used to love while others used to play.
Don’t ask me why, but time has passed us by,
Someone else moved in from far away.

Now we are tall, and christmas trees are small,
And you don’t ask the time of day.
But you and i, our love will never die,
But guess who’ll cry come first of may.

The apple tree that grew for you and me,
I watched the apples falling one by one.
And as I recall the moment of them all,
The day I kissed your cheek and you were gone.

Now we are tall, and christmas trees are small,
And you don’t ask the time of day.
But you and i, our love will never die,
But guess who’ll cry come first of may.

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Anyone knows what the following lines mean?

Don’t ask me why, but time has passed us by,
Someone else moved in from far away

...

But guess who’ll cry come first of may.

Answer 1

I guess growing up as a child, but now an adult.