Player-sexuality - while definitely the safest and most fair option - strips LIs of their sexuality (they can not talk about it or anyhow indicate. The good attempt was in DA2, when Anders had a special line for gay Hawk, but this is only one example I can think of).
I still do not understand why not take the next step and add sexuality for protagonist? You choose who your character is - gay, bi or straight - and potential LI reacts accordingly. A few lines changed depending on your choice would make the whole romance more believable, the existence of the sexuality will be admitted, and yet you would be able to get anyone you want.
I mean, you do already somewhat choose your protagonist's sexuality through your choices of who to romance. There doesn't need to be a specific flag that you choose at character creation.
I think a better option would be to add more dialogue options to when companions proposition you if you accept/reject them, including of course a "none of your business why I don't want to sleep with you" option.
