Post-fucking relaxing

Millie leaves my cock in her pussy after I have finished cuming, and I feel my cock slowly growing soft. Eventually she rolls of me, and lays to the side of me, slowly stroking my cheek. Neither of us say anything, but then finally Millie speaks and says:

"Was that as good as you hoped it would be?"

"It was even better Millie." I say, and try to kiss her, but she turns her head away, then looks back at me and says:

"Makes for better family dynamics if step-moms have their step-sons lose their virginity to them, don't you think?" Then she starts to laugh.

I laugh as well, not sure what to reply, then Millie gets up, and says:

"Well, it is getting late, we need to get back." Then starts walking back towards the beach.

I follow her in silence, looking at her naked ass swaying back and forth. We start loading up the kayak, both of us still completely nude, and then I finally work up the courage to ask:

"Millie, could we, you know... again?"

Millie stops what she is doing, looks at me, and says:

"Matt, what happened today on this island stays on this island."

I nod, signalling that I have got what she is saying, and we finish loading up the kayak, get dressed and then Millie climbs in and I push the kayak out from the beach until it is clear of the sand on the bottom, then I jump in, and we paddle away.

As we are paddling away, Millie says, without looking back at me:

"Matt?"

"Yes. I reply.

"If you are a very good boy, then we might go back to the island next time your dad leaves for a business trip."

I feel my cock grow hard in my shorts.