Looking for more information About Dan?
Dan is at a point of an open, polyamorous, V-shaped relationship with his partner, Ruth, and her husband, JTA. They live together at their house near Oxford along their two children (biologically Ruth and JTA’s owing to Dan’s sterilisation but co-parented). In case you’ve not come across those terms before:

V-shaped: there are two relationships here, “hinged” around a person in the middle. In our case, Ruth has a relationship with her husband, JTA, and with her boyfriend, Dan.

Polyamorous: polyamory is the practice of being in a multiple simultaneous negotiated non-monogamous relationships. It’s not cheating: everybody knows about it and they’re all okay with it.

Open: an open relationship is one in which the parties involved are free to date other people. Not all polyamorous relationships are open relationships, and not all open relationships are polyamorous. It’s complicated. The short of it is, Dan is both “in a relationship” and “available”.
Further reading might include:

Dan’s blog posts tagged polyamory, sexuality, relationships, parenting or children.
Dan’s blog post Polyamory As An Identity, about why polyamory is something he does, rather than something he is.

Wikipedia article about Polyamory.
The weblog of Ruth, Dan’s partner.
The weblog of JTA, her husband.

The Ethical Slut: A Guide to Infinite Sexual Possibilities, by Dossie Easton and Catherine A. Liszt.

Sex at Dawn: The Prehistoric Origins of Modern Sexuality, by Christopher Ryan and Cacilda Jethá.