Boyce and Alan?

What's the deal between Boyce and Alan? At the beginning I thought Boyce was just stirring Alan up, teasing him and deliberately trying to make him appear ridiculous during 'lessons', but then it seemed that there was a real kind of physical attraction between them, in spite of Boyce's relationship with Kim, and Alan's with Joanna. Both bisex?
What exactly happened after the slave auction? And when Alan went for his walk along the riverbank with Jonny from the camping site?
It was quite a touching moment in the final episode when Alan phoned Boyce from the phone box to tell him (in code) that he was 'heading west'.
Would be interested to read your comments...