1. The PC can engage in sexual relationships with any companion regardless of sex, which means the companions are all bisexual, which breaks immersion because it doesn't nearly reflect the reality of common sexual predisposition (the fictional setting doesn't change that). 1 in 5 non-straight options should be more than sufficient to be reflective of society.
no.
How does this break immersion? You (as a character) don't know they are bisexual. The people you are with are simply attracted to you. You talk about immersion, but you use information that your character doesn't have to justify it. It's also very easy to anger them so they won't sleep with you, on purpose or not. I know people TRYING to romance and have locked themselves out of everyone except the one they didn't want. I also think you wildly underestimate how many people have experimented
When Wyll constantly flirts with other woman but also hits on you (and only you) male character because you were nice to him once you know he is bisexual.
When the same thing happens with Gale after he talks about his love affair with Mystara you know it, too.
And when the gith hating shar priestess happily and easily sleeps with your gith cleric of selune you run out of excuses why playersexuality is supposedly not hurting immersion.