[What lips my lips have kissed, and where, and why]

This poem is one of my favorites. I say that a lot, but it doesn't make it any less than the truth. The way this was written just... Pardon the cheesiness, but it kind of just spoke to me--I understood it and I understood what was being said because, in a way, this relates on a personal level. 

Edna St. Vincent Millay didn't write this to be positive, that much is obviously clear within the first line we read: "What lips my lips have kissed, and where, and why." I automatically think of multiple partners that didn't mean much, because of the what, where, and why. If the partners meant anything to the speaker, she (presumably) would remember who she shared the kisses with. She would remember where, and why. But she doesn't. 

"I have forgotten, and what arms have lain / Under my head till morning; but the rain / Is full of ghosts tonight, that tap and sigh / Upon the glass and listen for reply."

My favorite part. It's depressing, it's heartbreaking and just screams loneliness and possibly regret, but it's beautifully worded at the same time, and almost seems to level out the dreariness. However, we once again get nearly the same message as the first line. She doesn't remember who she's been with, and perhaps she's regretting that, and wishing that the loneliness will wash away with the rain pattering against the window. Or maybe that's just me. An underlying message that we get is that she wants to forget her past lovers. They haunt her like ghosts and they remind her of all the mistakes and the regrets she has in her life.

The last parts of the poem is where we get a sense of finality to it all.

"Thus in the winter stands the lonely tree, / Nor knows what birds have vanished one by one." 

In other words, she's not as young as she used to be, and because of that she's all alone. The vanishing birds symbolize how all of her past company have simply left, presumably because she's just old. And at the very end, it's almost as if she's reminiscing; a bit nostalgic, even. She remembers everybody that's come and gone, though not in detail. She remembers what it was like, but she doesn't have that anymore. "I cannot say what loves have come and gone; / I only know that summer sang in me / A little while, that in me sings no more." 

This poem is so devastating and heartbreaking, but it also tells us a story about this woman who basically used up her time with people who didn't matter, whom she wouldn't remember later on in her life. I think that there's a lesson to be learned from this--to find somebody you'll remember. Build a relationship that will last, instead of building ones that will only last for a short while.