"Tomorrow"
The first kiss is his fault, and they both know it.
At the time it's her fault, of course, and he'll tell her that tomorrow. She'll laugh and sit up in the bed, coyly draping the sheet over her exposed body, pretending to be embarrassed.
He'll do the same, pretending not to be.
Tonight he'll take the blame. He'll pull away, and let her lean her forehead against his, wishing for their lips to meet again.
He'll fold. He'll grab her waist like she asks him to, and caress her face like he needs to, and by the time they're in bed he'll do whatever she says.
Tonight he'll act like it's his fault, and it is his fault, even if it's hers too.
But it can be her fault tomorrow.