My tuuurn-
I'm against something entirely different than probably most of folks here. Lets take a step back from playersexuality or set ones for a moment(I'll get to that in a little bit)- where's the focus going towards? Who are the romances being written for? The player, or the characters themselves?
Historically in games, the player.
And thats where I differ. In a world where I was writing romance options for a game, I would not want to appease a player, regardless of whom or what they are. I would write characters for the sake of themselves- I would make players have to WORK to get into these relationships and stick with them. Even players just like me.
Romances in games have historically always been "playersexual"; not in the "romance whomever you want" sort of way, but in the "romance is easy" sort of way. Pick Paragon options, done. Buy gifts, done. Pick whomever you want, done.
All way too easy. I want a degree of difficulty, and I feel the best way would be to write characters that are set in stone as far as their beliefs, histories, experiences, etc etc go. That includes sexuality, not at a single time, but across time.
So for example, say I'm playing a male character. There's this wonderful female character I want to pursue. Alright, cool. WELP- she's gay. And when I say she's gay, I mean she is totally, uncompromisingly, completely, and wholeheartedly always has been gay and that isn't going to change no matter what I do. Alright, friends it is. So, how bad do I want to pursue her?
Lets say a lot. Alright, next time, playing a female character. Solid. First hurdle jumped. Now, getting to know her, I'm learning her likes and dislikes. Ooh boy, looks like we're disagreeing. A lot. Is it too much? Is it enough that these characters can set their differences aside and keep trying? Would depend on the situation. Uh oh, the straw that broke the camel's back just came out of my character's mouth, and it wasn't at the top or bottom of some wheel either. Dang it. Well, she's a toughie.
I dig it.
I dig it because for too long, I've felt that yeah, romance in games has been fan service. That's weird. I disagree that the realism argument can't be used in a fantastical setting because while magic and dragons and trolls are made up, romance and a connection between people isn't. Rather than have romance be easier to complete than a 3rd grader's homework assignment, lets have all of our characters have to work to end up with the character they're interested in.
Sometimes, a character is just not gonna be into you. And I think thats okay. I think sexuality should be one of those things that keep certain characters from being interested in others, because it is a fundamental part of who they are as a person. Sexuality along with other parts that make up a character will affect how they interact with others. Its the difference between, "Hi, how are you?" and "Whoa...uh...umm...oh sorry, uh hi, hello, aww jeez I said it twice, umm...can I start over? Aha..."
When I have written characters for stories I've created in the past, even if their sexuality wasn't obvious or prevalent to the story at hand, I kept it in mind, because I knew that throughout that character's life, their sexuality would have in subtle ways affected how they responded to certain people, led them to certain places, did certain things, having a certain perspective others may not have, etc etc(Lord knows if my sexuality was different my internet history would be a vastly different field of battle)
Sexuality is an important part of what makes up who someone is. It doesn't have to be glaringly obvious, it doesn't require shouting it to the world, but in millions and millions of subtle ways normally looked over by the mind, it affects who we are and what we do. It doesn't make us any better or worse than we would be if it were different- it just helped make us the special little snowflake that we each individually are.
And I want the characters in my games to be those special little individual snowflakes taken seriously enough that something like their sexuality is accounted for in their writing, cutscenes, and what the player's character gets to interact with.
If that means playing a character that is totally different than what I would normally play, that is fantastic. That is great. Wonderful actually, in my opinion. It gives me reason to explore different opportunities, different archetypes and character personalities, with different histories and beliefs.
I'm imagining it now. A character in-game that is only attracted to the rule breakers and those that couldn't give a toss for loyalty or honor, someone who actively seeks those that are unfaithful to someone they're already with- that would be intense, and is totally against anything I would normally play.
But I might do it. I might replay my character as a scumbag who enters a relationship with one character just to drop them for another, secretly or otherwise(however it would be written). Exploring the options provided, and going out of my way to do so.
I want the characters I create reacting to the people in the World around them, and if that includes being cut off, I'm alright with that. I would hope that sexuality would be one of those potential cut offs, rather than being excused for the sake of me and my seven billion peers.
The game wouldn't be a romance simulator- it would simply make the links to reality in this fantasy game just a little bit more real. Though the argument can be made that it is its own reality, so what makes it feel real is different depending on how you look at it. As it turns out, this is my view. 
Though clearly from the extensive and many discussions held on subjects like this, I'd be crazy if I wasn't aware that there are many who disagree. S'all good. Great to see different opinions being shared. Please continue.