Coming out would shock my parents

Hey everyone!I know everyone gets stressed about coming out but I have been thinking a lot about it recently and, after many google searches, have not found people in a similar situation.So I definitely am not straight (not super sure on a label yet). But I I.D. somewhere under the bi umbrella and grew up attracted to boys (I'm a cis woman) and so my parents 100% believe me to be straight. One time, my mom even said to me, "I respect and support gay people, but when you told me about your first crush on a boy, I was relieved." Yep, that was an interesting moment.Any way, my parents are supportive of gay marriage/adoption/whathaveyou but sometimes my mom says biphobic things, asking particularly rude questions and making thoughtless statements about one of my close bi friends who is out to her. Overall, I need help with how to handle a situation where your parents are very supportive of other gay people but absolutely do not know that their child, me (HI), is a part of the community.I tend to share everything with my mom as an only child and I think if I told her, she'd feel absolutely shocked and maybe even a little deceived. I'm just really torn because I could just keep allowing them to believe I'm straight and not ruffle any feathers or I could come out and feel like I'm actually being honest.I know they wouldn't disown me or anything drastic but I just don't know how it might affect my relationship with my folks.Help me