Is New York City populated only by talky, insufferable singles who obsess over their trivial romantic entanglements? That’s the impression you get from Gray Matters, which centers on a romantic triangle involving a lesbian. The added twist here is that the competitors for the affection of marine biologist Charlie (Bridget Moynahan) are a brother (Tom Cavanagh) and his gay sister (Heather Graham). Bubbling along on a nonstop stream of self-conscious, “witty” dialogue, Gray Matters makes your average “Gilmore Girls” episode seem like a mime act. None of it comes naturally to the actors. Even the affable, stammering Cavanagh is obviously quoting an overly manicured script. I can only assume he’s not originally from New York.