I'm a hs jr who's just started getting into Shakespeare the past few weeks, and I've never been particularly into poetry, but I poked around at a few of his sonnets for fun, and the last line of this one hit me real hard, and has been reverberating thru my head since. I haven't read nearly enough of the sonnets to pick a favorite yet, but I'd be surprised if this one doesn't remain in my top few. Either way, this was a super informative video, and I'll definitely try to think about the concepts you mentioned while going through more sonnets (and plays, poetry, etc) :)
That you've taught lessons on it 100 times, but it seems like less and the sonnet is still fresh, says not only something about the sonnet, but something about your love for it!
The resolution is actually in the next sonnet, which is 65. 65 is the continuation of 64, where the black ink (poet's verse) will preserve his love (his beloved) beyond time.
Is he talking about his love for the poem, for the sonnet, and his fear that it shall die and never return and that it might not be immortal, eternal forever? That perhaps he equates himself with the poem and sees, finally, his own mortality? Possibly. In the news recently: "Florida school district to only teach excerpts from Shakespeare under new regulations. The full plays have been removed from the curriculum following the passing of a number of laws restricting sexual content in school reading materials."