The way I see it...the girls (aka, Darla and Drusilla) were away. Angelus and William, who were the best of friends, were back from the hunt, maybe drunk, certainly horny and said..."What the Hell". They spent a night together, with no-holds-barred and did the WORKS. In the morning, they just laughed it off, moved on and it wasn't a thing.
Liam had no friends. He was a drunk, the local rake and basically a slag. He was turned and just had Darla, then he turned Drusilla and had her too...but no friends. He turned Penn, but Penn was in awe of Angelus. He couldn't have a conversation with him. Drusilla siring William gave him the first friendship he'd ever had in his life/unlife. Annddd I personally feel that he tested the limits of that friendship by using Drusilla...are you really my friend, how far can I push you, etc.
It obviously worked, because they were close when tossed (held hostage) by The Immortal. And on the sub...were still friends.
I don't believe Spike was talking about himself and Angel having been intimate, post souls, but that was a reference to Angelus and either William or Spike. Now, it might have been friends with benefits or like I say, just a one-time thing that never became a big deal between them.
Either way, I'm glad fuel was given to Spangel...which by the way, before Yahoo! betrayed us all, I used to run a fan fiction group dedicated to. There were some truly amazing writers who contributed to it and I kept every single one of the stories that were posted to the group.
They do still exist on the websites that still exist 20-years later, but David Boreanaz has never had more on-screen chemistry with anyone than he did James Marsters and their characters produced the most amazing fan fiction of any fandom I've ever known.
It absolutely shouldn't be forgotten and I keep the fires burning with the hard work people put into the stories.
