I've got the same thing going on me. Some research I've done suggests that while with most people depression (or other things) sometime manifest themselves in a lack of interest in sex, with some it goes all the way to a complete lack of interest in relationships. Often, the start of this can be traced to a choice of sorts. For example, I was walking home from the library one day and I was thinking "This whole obsession with sex and getting horny and stuff, it's just a big waste of time. I'm done thinking about relationships. Period."
And just like that it was gone, and I haven't thought about it since.
How do you know? Well, at the moment, I'd just say I was straight if I were you, because that seems to be the default setting in the human species. But when the time comes, don't be afraid to try either side. You may just go a while without any feelings one way or another, and then suddenly feel attracted.
But don't worry about it.
