Advice needed - my queer bestie got a girlfriend

Hi, new around here, but hope this will make sense. So story time:
I'm a teenage girl and I've been friends with this girl for basically 3 years now. When we met, I was quite convinced I was aromantic, as I was convinced I've never had a crush before, etc. However, as we got closer, we started being very queer with each other, as it sometimes is with girl best friends. There was a very short-lived rumor that we were together, but she reacted badly to it, partially because she had a long distance boyfriend at the time. She had quite an interesting love life, she has had 3 different boyfriends since I've met her, 2 of which she dumped, the last one dumped her, overall she's quite non-committal, often talking to a few guys at once, but only ever committed to one. She always told me she's bisexual, and supposedly has had a short relationship with a girl at camp once, but largely due to a not super accepting family, she's never really been with girls, but she doesn't mostly live at home right now.
Over time she got more bold, she started kissing me on the forehead, etc., which felt nice. We had a sleepover, she fell asleep on me and in the morning we cuddled and I kind of realized I've fallen for her, and badly, and have since come to terms with the fact that I am in fact lesbian, which kind of does make sense looking back.
We kept getting more and more "serious" with each other, but still in a joking matter if you know what I mean - largely through e.g. sending WLW reels about being in a relationship, wanting to kiss, make out, missing each other, the likes. She started jokingly calling me her wife, saying "I'd prefer if it were you" when talking about something with her boyfriend, and so on
We had another sleep over, this time we ended up making out shirtless, and so I ended up with the outlook that we were genuinely quite serious
Now her last boyfriend dumped her, and it was the first time in a while she was single, and she said it felt weird, I met up with her, we talked for ages
Three days later, she texts me she's not single anymore, and that finally this time, it's not a guy, it's a girl who's a friend of ours. I told her 'finally', because her relationships with men have been awful, but I'm kind of sad, let me explain
I realize it's probably bad that we made out while she had a boyfriend, it did feel wrong post factum, but at the same time, she initiated it and I think there is no world where I would tell her no to that - I've always seen it as that she doesn't take relationships with girls seriously, as she e.g. can't take them home, be public about it, you know, so I've never thought about seriously suggesting she break up with her boyfriend so we can be together. She's said that if me, the girl who is now her girlfriend, or one other friend of hers wanted to be with her, she'd dump her boyfriend, but I said I wanted to be with her and it was never serious. I kind of accepted it as it is, that we can have this kind of non-serious queer platonic relationship, and her dating life will be men, but now that she genuinely has a girlfriend, I don't know what to think or do. She has always said that she'd love polygamy, as she doesn't get jealous and likes to have things with different people going on, but said she does know that most of the people she dates would never agree to that.
I kind of do not know what to do, it feels wrong to continue having this kind of relationship with her when she has a girlfriend, it felt different when I thought she was treating it as an unserious "I wish I could be with girls" thing, but I still love her, and she still is treating me the same way
Sorry for the long story, but any advice?