Like others have said a lot of what you're feeling may be internalized biphobia. Went through the same thing too personally. But here's something I realized that I keep in mind that helped put things into perspective: as a bi person your dating pool will always skew towards a "straight" passing one because they're are simply more straight and bi people of the opposite gender or other genders than bi and gay folks of your gender. That's just how the math works out. So statistically the average bi experience is a "straight" relationship from a shallow outsider perspective, but that doesn't change you, your partner, or yalls sexuality at all.

Being Bi is also not defined by enjoying your whole range of attraction simultaneously. There's a lot of things we all would like to do but realize realistically we just won't be able to, and that's okay. I love space but I know I'll never be an astronaut and go there, yet that doesn't make my desire to see the stars any less real and valid.

NTA. Both are young adults and would have figured it out anyways when they see mom is now living with a brand new guy all of a sudden. She did this all to herself and just wants you to share the raging guilt.

Pro tip: increase your odds by blasting Free Bird till the car starts shaking

Please for the love of God end this geritocracy

Jacob Gellars work is all gold
https://m.youtube.com/watch?v=ntLc4hHWqHs