They could have waited a month, for Valentine's Day.
But maybe they couldn't wait.
According to this preview of next week's Batman #15 by Tom King and Mitch Gerard, Bruce Wayne and Selina Kyle finally express their love towards each other. In the only way they can.
And, you know, have sex on a rooftop. Because that's what both of them always do as well. And they talk about their shared history.
"Ah yes, I remember it well…."