The entire fic is so sweet, you're almost guaranteed to catch diabetes from reading it.
In chapter 62, after Harry is killed by Voldemort, he meets his parents for the first time.
It says something about his House's loyalty to him when several Slytherins come to Harry's aid and claim him as their own simply because Snape is Harry's guardian.
Chapter 33: Harry chooses Snape over Sirius. Sirius accepts it. Snape faints.
Lupin sums up why Sirius isn't going argue about it quite nicely:
"Severus, you saved the only thing in this world that Padfoot really cares about. You did it when Dumbledore wouldn't and Sirius couldn't and I didn't. You were the only one there for Harry, even though you owed him nothing and could only feel hatred towards his family. Sirius and I know how much we owe you and that you are - despite being a 'greasy Slytherin git' - a very good person. Much better than us, in factů Like it or not, Severus, you're a Marauder too. You're part of our Pack."
Chapter 36: Snape tells Harry he loves him. In fact, are Harry and Snape in a room together without someone trying to murder them? Chances are, it'll become this.
Chapter 41: Harry's Essay about "His Da". Makes you feel all warm and fuzzy inside and get a little teary eyed as well.