Get your heart melted by the concern in his eyes and tell him yes, and then thank Sebastian for his offer.
You can't resist Darien so you say "Yes I'd appreciate it if you helped me home." Darien steps to your side and puts his arm around you. You turn to Sebastian, "It was nice to meet you and thanks for the boat ride, maybe I'll see you around." Sebatian smiles "Ya, and it was nice to meet you too." He then heads back into the park. You and Darien head back to Lita, Mina and Ami, with Rai trailing behind you. Then you all walk home together. The day didn't turn out too bad, in the end.
This is one of the seven endings of this story. Its one of the better ones. So you did very well.