We have people in this very thread talking about their experience with people who were faking it being gay. I think there was also another guy, didn't find his post.
...so?
In most situations, we acknowledge that engaging in faulty, negative generalizations reflects a counterproductive cognitive error - something happening in this specific instance, this specific situation, does not mean it'll happen again and again and again, especially when most evidence points otherwise.
Obviously, we expect our significant others to have fully realized friendships, right? And we
don't expect all those friendships to be with people with whom there is no potential for attraction. Usually, this all works out fine. You and your romantic partner each have your own lives, you share one another with your friends, share your friends with one another, and it is all good and healthy.
When your significant other is suddenly lying to you about their friends' sexual orientations, there are other issues at hand. Presumably, you're with someone because you see them as a good person, and your relationship with them as a good relationship. Sometimes that either turns out to be wrong or stops being right, but not trusting them to do things that are normal in most friendships (and that might be
very normal in their friendships) isn't the thing that will make it better.
Also, another thing about engaging in fruitless generalizations: emphasizing the "faking it being gay" stories when we all know
the vast majority (an understatement) of people who say they're gay aren't doing so with some nefarious intent is sort of bizarre.