This has shifted to MM, but I'm responding here because I'm not sure it would link if I changed the subject line, and because who knows, it may prove to have some bearing on the events of Raising Steam.
=Tamar wrote:It was indicated in MM that they [edited for clarity: Moist and Adora Belle] had been living together, both in his Post Office apartment and in the rooms at the Bank.
I don't see any indication in MM where Moist and Adora Belle were living together. In fact, throughout MM events kept happening in the book that prevent them from getting in a bit of fun. Adora Belle comes from a very strict family and most likely still lives at home when she's not digging in the field looking for lost golems. Certainly there wouldn't have been enough room at the post office for her to live with him (and Mrs. Maccalariat would certainly not tolerate such a situation) and his tenure at the bank was such a short one (only a few days) that she wouldn't have time to move in. And if they had been living together, Gladys would have been aware of the relationship and thus would not have developed her crush on him.
I'm not so sure about Gladys; I think she didn't get the book on etiquette until after Adora Belle had already left on her expedition, before MM began. She may have developed the crush before then.
The hints I saw in MM are subtle. Here's what I found on looking through the book again; page numbers re from the US hardcover edition.
p.7 "What Mr Lipwig does to get out of breath in his own room is his own affair." He was alone, but this indicates that the male part of the subculture of the post office would officially mind their own business and ignore any visitors he might have, while no doubt gossiping mightily.
p.247 Adora: "I'm going home for a bath." Point to you, they apparently are not living together. But I still say they are sleeping together, no matter what Mrs Maccalariat might say.
p.269 Moist tells Gladys that Adora is his fiancee and will be spending a lot of time at the bank. Gladys's eyes dim.
p.275 Gladys is cooking dinner for Moist and is defiant about it. Why? Peggy is looking for Mr Fusspot and presumably has asked Gladys to watch the pot, but why didn't Gladys say "I'm watching the pot while Peggy is searching for the dog"? "I'm cooking dinner" is an attempt to claim a relationship with Moist, and this is right after she found out that Moist has a fiancee.
The strongest evidence:
p.298 "Lying here now in the darkness of the bank..." "He was alone because Adora Belle was spending a night in the cells for assaulting an officer of the Watch."
p.362 [and the first page of Chapter 13) "...Moist von Lipwig woke up...but woke up alone, which was less pleasing." (He's back in the Post Office while the bank is being investigated.)