I think it is a positive step forward giving each companion their own sexuality rather than defining it by the player. It was annoying with DA2 coming to the forums and seeing people going on about how traumatised Anders must have been by having to kill his former lover, etc, and me thinking, what? Because you see my first Hawke was female and that aspect never came up in conversation because for her he was straight.
I think Dorian will probably raise his sexuality fairly early on because it is part of the reason he had to leave Tevinter, why he is considered a pariah by his family. Naturally as a PC I would wonder why someone from a powerful Magister family would turn his back on it. He might have come to question the system even without the added complication of his sexuality but it may be that it was his family's attitude to this that made him start to question everything else. Obviously once we get to talk to him that will be made clear. It would seem far more natural for something to come up in the context of his history and then leave the option open for the PC to pursuit it at a later date or for him just to say (Zevran style), do you think it could ever go anywhere between us?
I'm hoping it will be more like this rather than DA2 method of heart icon, click. For a start off I found the introduction of the flirt option on practically the first serious conversation you had with either Anders or Fenris really crass. We had Anders explaining about his relationship with Justice, which was a really difficult subject, and then suddenly you are hitting on him. Likewise, after Fenris has just told you about Danarius wanting to strip the skin from his body. Yet first play through I couldn't be sure if avoiding taking that option would shut off romance altogether.
In ME3 we actually had to two different approaches, one of which worked, the other didn't. The first was with Steve. I don't know what happened if you weren't in a relationship but my male Shepard in a romance with Jack, made a flirty comment at the nightclub, to which Steve replied that he knew I was just kidding because I had a girl friend. To which I replied, yes you got me, or words to that effect. So Steven took it as just a bit of banter between friends and that was an end of it.
The second, which didn't work, was with Kaiden, when it seemed that purely on the basis of visiting in hospital and giving him a gift, suddenly when we're having a friendly chat in the Citadel he was confessing his love for me, even though I was in a romance with Tali. That made me feel really bad because I had no idea he was even gay, let alone I had inadvertently given him the come on simply by being a caring friend.
So I'm really hopeful that the Dorian romance arc will be treated in a way that develops naturally and that it is also possible to have a close friendship with him, either male or female, without him taking it the wrong way.