I read this fic here years ago. Buffy is one night stand kinda girl, Spike is an artist and after they had sex he invites her too his art show. Also I remember his mother dying and Buffy ordering tickets and renting car for him, going to him later. Also Buffy was raped by another artist. Spike hit the guy and takes care of her. I remember Buffy finding huge painting of heart and understanding he is in love with her. Later in fic Spike uses ashes of his mother as base for his painting. And remember Spike using excersising half naked to seduce Buffy.

this popped to mind.

One Special Night by Katrina

https://dark-solace.org/elysian/viewstory.php?sid=1877

ForgottenYogurt
Sorry not the one. There wasn't much of other BtVS characters. Oz was Spikes friend and they had one showing together. Oz made sculptures I believe. Possible Giles was Spike dad but not sure. There was no Willow or Dawn for sure.
No wedding ever. By the end of story Buffy was making tentative steps at having sex life.

You should check out 'Something Real' by Dampersandspoons (aka Grief Counseling).
Hope this is the one.

Hannora
You are genius!!! That's the one ??