I have a couple questions about the Rome Decoy
1. What happens to the "Buffy Summers" in Rome?
2. Does The Immortal know he's dating a decoy?
3. Does the Rome Decoy have the exact face of Buffy Summers? (sorry for the stupid question)
4. Who was the Slayer's identity decoying as Buffy?
And, if I might be allowed to add a fifth question,
5. Why was this charade necessary in the first place? We learn in the first issue of Season 8 that it's some scheme that Giles and Andrew cooked up, but why? For the life of me, I can't imagine that, surrounded by a battalion of eager young Slayers as she was, there could be any reason to conceal her true presence for her personal protection, so, what does that leave?
Anyhow, as for the original questions:
1) All that we know for sure is that she was cavorting around town with the Immortal, who, or WHATever he is. Why? We will probably never know. Dammit.
2) I would say, probably not. To my way of thinking, and this is pure conjecture, his sexual conquests are very important to the Immortal, and having the Chief Slayer as his lover is more of a status symbol than anything else (no offense to Buffy, but there are probably thousands, if not tens of thousands of more skilled courtesans in the world, and, supposedly, the Immortal would have his pick of any or all of them. Why settle for a relatively inexperienced girl? To taunt Angel and Spike? Unlikely)
3) Almost certainly, the decoy Slayer bears a very close resemblance to Buffy, but I doubt that an exact double would be necessary.
4) The Roman decoy is obviously meant to be as anonymous as the underground Buffy was, so I seriously doubt that we will ever know who she really is.