If they're shagging (and reading between the lines, they were), then they must be sexually attracted to one another, and they're of the same gender. Surely that makes them gay? Or, more accurately, homosexual, at least, if you want to remove any implications of a particular lifestyle that "gay" carries.
(, Wed 8 Jul 2009, 13:45, archived)
without knowing exactly what motivations are behind it. Pair bonding covers far more possibilities such as co-operation to protect territory or to improve social standing or boredom/frustration or liking a bit of cock. It also doesn't distinguish it from heterosexual relationships which may serve the same ends aside from procreation in other circumstances. It's suitably fuzzy I think.
(, Wed 8 Jul 2009, 13:59, archived)