Pretend you didn't even hear him and continue on with Sebastian.
You don't even look at Darien and start walking saying to Sebastian, "This way." So you walk home wiht Sebastian and leave Darien behind. The day didn't work out exaclty as planned, but her look on the bright side you didn't have to fight any monsters.
This is one of the seven endings to this story. There are ones that are alot better. But hey, at least you can start over.