I think both of Andrew's Season 5 appearances are fictive to some degree. In Damage, using his clownish image to disarm Angel and his gang so he could double-cross them. (I also think he was gathering intel about the gang's behavior and purpose in joining WR&H). In TGiQ he was, at the very least, furthering the company line about Buffy being in Rome. Though...
I have a personal theory that the true purpose behind all the wacky shenanigans of TGiQ was part of an ongoing operation against The Immortal. I think Spike and Angel were used to distract the Immortal for the night (with the faux!Buffy providing a secondary distraction) so that Andrew's team could infiltrate The Immortal's home or operation.
But, regardless if that's true or not, I think that Andrew had planned on letting Spike and Angel in on the joke when he first set the seeds of it on Damaged, but that by the time TGiQ rolled around he was pissed off. There's no one in the Whedonverse who's a bigger supporter of Spuffy than Andrew, and having Spike (and Angel, but Andrew doesn't really know or care about him) show up all "I love Buffy and must save her...from this other guy!" so many months after he'd promised to tell Buffy he was back and hadn't, made Andrew decide to leave Spike hanging for a bit. Who knows if Andrew would have let Spike know the truth if they all hadn't gone rushing into a suicide mission a week later.
Regardless of whether or not you like him as a character, I think you've got to accept that he's grown somewhat. He's allowed his own slayer team, he's in charge of operations, he's trusted with perhaps the biggest secret of the New Watcher's Council, etc. He's the newest member of the Scooby Gang now, and not just a tag-along.
