The Museum of London has a growing collection of material and oral histories relating to gay lives. A good sample can be seen on their 'Reassessing what we collect' site here: http://www.museumoflondon.org.uk/English/Collections/OnlineResources/RWWC/Themes/1161/. Although much of the material is modern, it also touches on Roman London - with a coin representing the homosexual Emperor Hadrian, and to the eighteenth century with an image of a cross-dressing woman.