Hi guys
I have a fic in my head and I can remember a lot of details but not the title or author and it's driving me insane!

Buffy and Spike (who's wealthy) have an affair, Spike is married to Drusilla and Angel is their son. I remember Buffy going to a party to see Drusilla and there she talks to Angel. I also remember a scene where Buffy and Spike have s e x (can't use the actual word because of spamming issues) and she says "don't treat me like one of your kids" and he says "this isn't how I treat my kids". And he is wondering why she's suddenly bothered with him having children.
Buffy ends up trying to leave, she goes to the airport and everything, only she comes back to their appartment where he is still sitting on the couch.
Please help!