As is standard practice for Law and Order, very little of anyone's personal life is ever directly revealed. In general, all things of a personal nature are brought about either in some sort of cross-dialogue or by passing visuals only. Example, during one episode Jack McCoy is shown carrying his motorcycle helmet (the meaning is somewhat inferred, etc); I think in another episode he's seen briefly leaving a pub, arm-in-arm with a woman, clearly on a date, but gets picked up by Fontana and Green when it's discovered there's a hit out on him, and the direction instantly changes, etc. etc. Serena is never shown on a date with a man, she never ever mentions a boyfriend or a male love interest, she is never hit on by anyone ever except a plastic surgeon (who really isn't hitting on her, just her $$$) ... Add to this the fact she has a palpable and at times barbarous relationship with Aurthur Branch, usually cropping up snidely regarding any legal handling of any social policy that's left-leaning and isn't getting more of a liberal consideration. So, I was not at all surprised by her sexual orientation, I was, however, surprised at how it came out into the open so abruptly at the time of her termination. Personally, of all the female ADA's on this series (Mr. Robinette was the only male of the slew ever), I found Southerly to be the least sexually attractive, and the weakest actress, overall.