This is going down a deep dark road but I'll reply this one time 
I prefer gated companions simply because it's unrealistic if everyone is PC-sexual like they were in DA2.
They were bisexual in DA2. I can assure you that bisexual people are perfectly realistic 
But even if they were confirmed as PC-sexual, they are characters, not real people. A writer can change a character's sexuality quite easily. And in an RPG, you are, to some degree, the "writer" of your character's story. So in my Hawke's story, Fenris was gay. I can replay with a female Hawke, and in her story, he is straight. I can replay a third Hawke who romanced Fenris but dumped him for Anders, and in his story, Fenris later hooks up with Isabela, and thus is bisexual.
What your orientation is informs a lot about your and how you behave.
Not really; I mean sexuality doesn't chemically alter how you think or feel. Now depending on your environment, say if you live in a place where being gay is considered immoral or wrong, and you are therefore persecuted, it may shape how you see the world and react to it.
But no, your orientation doesn't affect how you behave. If we're speaking strictly biological factors anyway.
Think about Dumbledore's backstory in Harry Potter. There was a lot of complexity there, enough that people were hotly debating his orientation. I'll admit to being annoyed when Rowling outed him because, frankly, that detail was unnecessary to the stories themselves even though it makes perfect sense when you look at his backstory again. You honestly don't need to know the orientations of any of Harry's teachers for the stories to work setting aside Snape for whom it is central to the plot, not even Hagrid although it provides an amusing side story.
I would not consider Dumbledore's backstory particular complex lol Rowling doesn't really do... complex characterization
The only problem I have with Rowling "outing" her own character post-publication is that she should have made it blatantly obvious that Dumbledore and what's-his-name were a couple; it was cowardly to do it after the fact.
However, to write a really good character, you do need an idea of these things for them.
Well, yes lol However, choosing to make a character bisexual does not make her "less real" than if you had chosen to make her straight.
However, if you decide to scrap that original story, and rewrite the character in a new story, but this time make her gay, she is still the same character. Maybe you've placed her in a world where being gay is severely stigmatized, so that will affect her narrative. But she is still essentially the same character as when you wrote her the first time (assuming you changed nothing else).
We're getting close to 4000, right? I'm grading finals so I should shush now 