When Joanna (Amanda Ryan) waits for Chris (Christian Bale) to join her in bed, around 1h22, she's clearly fully nude. But when she exchanges a few words with Chris after he makes a quick stop in the bathroom, one can briefly see that she now wears panties (given the context, she absolutely had no reason to put them on meanwhile).
When sitting in the Pub talking about sleeping with "other" women and having sex with the same person for so long, the song heard on the juke-box in the background is Dire Straits' "Sultans of Swing". Although an early version of the song had indeed been recorded in June 1977 and even received significant airplay in London, the particular version heard wasn't recorded until mid 1978.