The rules for falling for your best friend:

Don’t.
Forget the crush you had on him when you were eight.
And when you were thirteen.
And again when you thought he fell for someone else.
The real rules for falling for your best friend:

Break the first rule.
Let both of yourselves be shameless.
Try out each flat surface of your house to see if the heat is still the same—Spoiler, it is.
Fall for the man he is, not the man you thought he was.
Remember the first rule.
And know he might have fallen first.