Memory Lane.
This hadn't begun when Dawn dragged his drunken arse through Sunnydale, escaping a brawl started because some idiot had ogled her.
It hadn't begun when she'd secretly hunted for him in L.A.. Back then he had sworn that Angel, prophecies and destinies were a mere annoyance when compared to her anger.
Then she came back, tired and wishing to forget her freaky former life. She called him and never noticed that their friendship was the freakiest of them all.
Spike cannot pinpoint the exact moment it started, but with the slim brunette cuddled against his side, he doesn't really care.