It's stuck in my head so bad, and I've been looking for about a month. This is an AU/All human fic where Buffy and William are in love, but someone is trying to kill her. She fakes her death in a car bomb and leaves with Giles, who is her bodyguard. She comes back a year later with William's baby and he's furious with her.

That's all I have. Don't know if it's finished, gone forever, or I have a really weird imagination!

It's called Over the Summer by SlayerFan

https://m.fanfiction.net/s/1243580/1/Over-The-Summer

Totally it! Thank you so, so much!