Telephone Wire, from Fun Home - the way she's in that position of memory, begging her past self to say anything to her dad that might open him up, even though she, and we, know that that's impossible, because otherwise the show, and the pain, wouldn't exist. I was a mess when I saw this on tour.
Children and Art, from Sunday in the Park - "Isn't she beautiful, there she is, there she is, there she is, there she is...mama is everywhere, he must have loved her so much" is one of the saddest and most beautiful lyric lines ever put into any musical. It says so much about love and time in such a strange way, the emotional and conceptual epiphany always catches me off guard.
The I Love You Song, from 25th Annual - The absolutely devastating desperation knocks me over even when I'm just listening to the album while doing chores. When she spells the word and we hear "that is correct" in a distant echo, and then she and her parents sing the last notes in perfect, imagined, and impossible harmony, my heart aches.