Cassandra sees your apartment from afar, while she hopes that you will at least go out and see through the window how she watches you, even if you don't know that she is Batgirl.
She never wanted to break up with you, but you're practically her weakness, and every weakness has to go, right? However, even if you are her weakness, you will always be her favorite weakness. Being Batgirl is complicated for Cass, she never told you that and it seems like she never will tell you. You are hurt, with no reasons why she broke up with you. Cassandra feels guilty.
Until she got tired.
She goes towards your window in a leap full of elegance worthy of a ballerina, as she falls right on the fire escapes, right in front of your window. She silently opens the window and, there you are, lying, sleeping peacefully in your bed. Cassandra's desire to go to sleep with you and hug you is unimaginable.
"I'm sorry," she whispers, hoping you won't even listen, but at least she said it. She doesn't want to wake you up, but she also doesn't want you to be left wondering why she broke up with you.