Afraid of Vulnerability (Fearful Avoidant Attachment)

I've started to realize that I'm afraid of being vulnerable. I know it's very common for FA's to dislike vulnerability, and to avoid it, tho I feel like I avoid it for different reasons. I've heard some FA's avoid vulnerability because they're afraid it'll be used against them, but for me, it's because I'm afraid that if I show too much vulnerability, I'll be annoying or seem insecure. Growing up, I wasn't allowed to really show vulnerability, and have memories of my family rolling their eyes and saying me seeking reassurance was "annoying", and that they were "sick of it". One time they even told me, "We don't care about your feelings.", which obviously seem to have affected me. Tho, I didn't think it would. I have these two friends I've been talking to for a few days, and I really like them! But they've started to trigger FA stuff, and I've realized I've had a bit of a fear of opening up to them. I opened up to both of them some of my boundaries. I'm an introvert and value my alone time a lot, so I told them that, while reassuring them it wasn't because of them, and they handled it great! But I started to feel this anxiety? I started worrying that one of my friends felt rejected or upset by me doing that, and so I went to her, asking her for reassurance to see if she felt that way. She told me she didn't and that she doesn't mind time away at all, since she's introverted as well. That relieved me, knowing she didn't mind, but I started to feel anxious about something else. I started to worry that I was "doing too much", and that my constant vulnerability must've been annoying to her, or that I'm throwing some sort of a pity party. I felt so insecure after opening up and asking for reassurance. When she was distracted and I sent her a text, my mind starting saying "she's not replying to you because she's annoyed by you. You're driving her crazy.", and tho I shook away those feelings, they were strong. So, I've started to fear vulnerability more, and I'm afraid of showing vulnerable sides now. I don't know what's healthy vulnerability? When should I show vulnabilty, when should I self-soothe? Is this normal vulnerability? I was never taught this, and was only shamed when I was vulnerable, so I just feel like a burden when I show it? Keep in mind that I've only known these people for like 3 days: is it too soon to show vulnabilty? How can I learn vulnerability? Is there any books about it or??