I should be excluded from the only community who has ever understood me and given me safety
If your "community" would exclude you for being bisexual, you should take it up with them.
A lesbian space should not be excluding bisexual women with female partners, just as a vegetarian space should not be excluding omnivores eating plant food.
The spaces are set up to allow people to perform the activity - women being with women, or people eating stuff other than meat. They should not be "identity"-based or exclusive because identity is bollocks. But they should have clear rules about what happens in the space to suit the people they're intended for.
If they were to exclude you for trying to take a male partner along, then that seems perfectly reasonable, just as a vegetarian space excluding me for bringing my sausage seems reasonable. (Whether or not I lie about my sausage being plant-based).
There are a squillion non-lesbian and non-vegetarian spaces. Not taking a male or sausage along to your favourite lesbian/vegetarian space is just being a decent person, and letting those spaces be used as intended.