I don’t know how to react to this

Hi, so I have been with my boyfriend for several years now and his brother has been dating a girl for a little while. But I but I have this issue with her and it’s frustrating me so much that it bothers me in the first place and it’s that she’s too affectionate towards me. I actually get so annoyed and bothered by it that it flusters my social anxiety after I get annoyed to the point of anger. At first, it was okay because she’d get drunk and only try to hug me a little and keep saying “I love you”(I barely knew her for more than 2 weeks at the time). And I talked to my boyfriend about it and apologized saying that she was very overly affectionate and had some issues, but she was harmless. I started thinking that it just had to be me and I just wasn’t a very affectionate person when it came to new people(especially if I don’t really know them). But she kept doing it the handful of times I saw her, and eventually it got to the point where I just avoid her other than being polite to her. Now, I was in a immigrant household and understand my upbringing and social conditioning may have been different. So I understand if maybe I’m misunderstanding some social norms. I do remember meeting some other white American women who were so quick to say I love you so quick when becoming my friend that I saw it super weird and almost forced, but I assumed it might have been part of the culture to say the phrase really casually and in my culture we tend to say “I really like your vibe” or “you’re fun to hangout with”. But saying I love you is for family, close friends, and partners. So I wonder if this is a cultural thing or do I just have more boundaries because of my social anxiety. I really hate confrontation, but I feel I need to express my discomfort. She appears to be very sensitive and easily hurt, so how would I go about letting her know, without hurting her? She’s really quite nice, just too much for me sometimes