Since I dont know anything about how confident you and calm you are before, during and after having sex with 'the girl' its hard to give you a good advice on what to do.
But I'll try.
From my own experience you have the chance to create something more solid by using diffrent methods if we're to call what Im doing I'd call it "The playful method".
So what do I mean by saying 'playful'?
Well, its all about making the sex part something you both are cool with, something you enjoy, something that is natural. I think thats the way to go.
Example:
2 Weeks ago I met this girl at night club. Yada yada yada...
We are having fun and she comes with me home.
The next day I wake up and she is in my bed. I remember we had a good time and when she wakes up we start talking bla bla bla.
Im like laughing and telling her she's smooking hot and I am to rate or drunken sex act it a definte 7/10... she punches my shoulder says its not fare...
The point is: we had sex, its no biggie, we can talk to each other the next day, even though Im 100% complete souber I can still be the cute guy she met the day before.
I give her my number, before she leaves Im like: " 7/10 is definetly worth a High-five..."
She laughs, kisses me, leaves...
Later that night she texts: "Your 10/10
"And then its done.
Its playful and nothing I say or do can go wrong.
She came over 3 days ago after I texted her: "Wanne make out and watch a movie as an excuse for having awsome sex?"
If you can find the playfull way of behaving things doesnt have to be that serious, and the girl will keep feeling attracted since your a calm, interesting, non-needy guy.
I hope this, in someway, can help you.