Maybe it's just me, but this is a somewhat questionable line of reasoning. Bisexuality doesn't mean that the character is more likely to cheat nor
. . . nor did I suggest that they were.
" . . . nor more likely to want to engage in a three some."
. . . nor did I suggest that they would.
Examples of potential complications are not, "What every bisexual person who ever lived would do." They're just that. Examples of complications that 'a' character of this persuasion might have, not examples of what 'every' bisexual character would do. Automatically taking something written or spoken to the most extreme interpretation possible, that it's suggesting all bisexuals would be unloyal or want to be involved in a threesome, is quite odd really. If I'd meant 'every bisexual is like this' I'd have said it exactly in those terms. This is called putting words in someone's mouth, when one gives an example of a complication for 'a' character and 'a' complication (or two) and the reader takes the complication as applied to all person's sharing aspects of the character.
Yes, these plot lines could happen with a bisexual character, but they could also happen with a straight or gay character.
Nor did I suggest these complications couldn't happen for Straight or Gay/Lesbian characters. If you'd like me to buffer all statements with a long line of lawyer speak listing complications, characters and all possible combinations before every post I can do that. It would, however, make for some rather tedious reading.
Now, what I actually was saying with this is much simpler, that a bisexual person isn't going to change their preference for 'you' anymore than a Gay/Lesbian or Straight character is going to change their preference for you. Hence the examples of complications that challenge a, "They may be bi, but I'm the protagonist, and now they're exclusive to me and any feelings toward gender beyond mine suddenly go away" which is the actual faulty logic.
Not to say a Bisexual person can't be loyal, nor is to say they that they must want multiple partners, but it's also too easy for developers to turn a character that's supposedly biseaxual into a character that just likes whatever gender the protagonist is. Anything that challenges, "I'm the protagonist you have to love me because I'm the protagonist" lines of logic is, in my mind, preferable.
Wow. That's really gross. Like really offensive and gross. Attraction to both sexes doesn't necessitate acting on said attraction. Presumably straight people, even married ones, still become attracted to other people in their gender of preference.
You too can put words in my mouth that I did not say. See above.
"So, why do people assume"
Why do you assume things that are incorrect? Probably for the same reason everyone does. People are flawed, but since perfection is neither possible nor interesting I'm perfectly happy to leave things as is. An [incorrect] assumption, on the part of several posters, about what I was saying lit a fire in the thread, and caused an entire line of discussion that perked it up a bit. Personally I find that more interesting than if everyone agreed with everyone. I wouldn't change a thing.
Personally I wish Bioware would let male avatars have more effeminate physical traits to choose from, in addition to the current, as well as features like long hair, make-up and other portions. I've never been much into the large bulgy muscled, gruff and gritty and all that . . . but many developers and publishers 'assume' that's what any male audience wants out of their male characters . . . (unless we're talking eastern developers, and select few western developers) but that's another thread.
Hilarious that you should mention Tali, since there is literally no reason why FemShep can't romance her. She has all of the dialogue leading to romance, and she's every bit as sexually frustrated with FemShep as she is with Sheploo. So they did exactly the opposite of what you're commending them for- they laid the groundwork for her to be bisexual, but pulled back at the last minute with no explanation.
They did something similar with Jack, where she says she's bisexual but she has no interest in FemShep, only Sheploo and his Healing ****. Also ridiculous.
I always did find it interesting that they set that up, but never delivered on it. If the Developers ever commented on why I've never been aware of it. I'm sure it would be an interesting read. Jack I tend to understand more, given a few things prior to my reply to your post, but I recall Tali seemed genuinely interested at a few points. I suppose it could be as simple as, "They reused male Shepard lines" for some reason, without the intention of going in the direcion . . . but . . . eh, who knows but the developers? Certainly it isn't for me to say.