Based on Separate Beds by Lavyrle Spencer

Looking for a fic that is based off of the book by Lavyrle Spencer, Called "Separate Beds". Spike is rich, Buffy is from a poor/drunk family. They meet on a blind date and sleep together. Buffy gets pregnant and marrys Spike. Xander is her older brother/guardian who is a drunk. He threatens Spike, his father Giles and Buffy for money. He wants Spike to marry Buffy and take responsibility and also wants money from the family. They end up falling in love in the end.

Got any idea? I am pretty sure that I read this story here...

That's 20 Month by Machine I think.

SUMMARY: Buffy and Spike share a drunken night then decide to marry after Buffy finds out she is pregnant. They don't love each other. They barely know each other. But they marry under the agreement to divorce one year and one month after Buffy gives birth in order to keep Buffy and the child away from Buffys abusive parents.

Is that the one? I know both, the book and the story; the story is a bit different but based on it.
*edit* It says in the German translation that it is based on the Book by Lavyrle Spencer.

Since the original poster hasn't replied, I'm moving this to 'found' if this is not the story then let me know or simply post it here and I'll move it back to 'find-a-fic' section.