All Human-Old time I believe Spike is a lord/duke and he takes buffy to be his mistress

This fic is set in not medieval times but in the past. All human. Spike/William is a lord or duke some form of power. He somehow acquires Buffy as his mistress or to-be wife but he is evil and not nice. She hates him but has to stay. They go to a party and Angelus is with Darla but takes an interest in Buffy and I believe he kidnaps her at the end. Spike saving her. Oh, Spike and Angelus or Spike and hank are both sleeping with Drusilla...

Is it this one?

The Lord and the Lady by Gillypod

http://dark-solace.org/elysian/viewstory.php?sid=1555&warning=NC-17

Summary: Lord William must marry for money, but can he marry and keep his mistress Drusilla. AN: My story is set in the English Regency era with the date about 1815. The story revolves around the son of a penniless Duke (William a.k.a. Spike) and a rich debutante who is also the daughter of a Duke (Elizabeth a.k.a. Buffy). Elizabeth is of a mind to marry for love and William is just as sure that he needs to marry for money. William is determined to hold on to his mistress of 10 years, Lady Drusilla Angelus, and although attracted to his intended he is sure he can love only Drusilla. Will Buffy remove Spike from Drusilla's clutches or will he return again to the arms of his Dark Princess.

Thank you!

I really love that story. Glad I could find it for you.