Madeline

You are a guy.
You have a friend Miles.
You've been friends with him for quite a long time (about 5 years), and Miles has a younger sister, Madeline. She's 17, you and your friend are 19.

You always treated Madeline like a little sister... you called her Mady, you could take her or pick her up from anywhere without any problems, and at sleepovers the three of you always fooled around.

In short, there's no hint of love. Or are you just forcing yourself to believe it so as not to ruin the friendship?

Madeline has become closer to you lately, Miles, to be honest... and now, it seems, she feels something mutual. Go for it.

you are getting hints of a love relationship