Camberwell mentioned earlier, but Borough Market is a nice way to spend a morning (I think it's only Friday and Saturday morning). And can wander along to Tate Modern if that's your thing. And can wander a bit further to South Bank, where there's usually something on in the summer.
I would also recommend going to a show (not necessarily a gay one), but would recommend taking in one of the smaller theatres. For example, The Almeida, in Angel where I live, is an excellent little venue for dinner and a show. Or lots of the pubs also have an upstairs theatre which is quite quirky and inexpensive.