How do I (19F) have a friendship with my ex (19F)?

I’ll try to keep this short but I might not as I am currently high. I need advice on how to be friends with my ex-girlfriend. For some context; We broke up around five months ago, because she did not really know herself outside of our relationship. I can totally understand that, as most of our friends referred to us as a whole, and I can admit both of us didn’t really have our own identities outside of “us.” I was fine with being us, and she wanted to be her, I get it. We moved away from our hometown for college and lived together, we even got a cat. Then she broke up with me, moved out, then the college year ended (I kept the cat, she is very lovely). I know I am young, but I thought we had that high-school sweethearts kind of love you hear about, we dated for three years total. The breakup blindsided me, I will admit.

The problem is we have the same friend-groups, some of which were originally my friends, some were hers. They are separate groups of two each, and I can say we each hang out with one group more, albeit separately (with originally my friend group). We haven’t hung out within this friend group but eventually it I think it will happen. They offered to not be her friend anymore, which I denied, and even encouraged them to stay friends with her. She is a very sweet girl, and I have nothing bad to say about her. We did try to hang out for a birthday dinner, to where I got too drunk in the restaurant, and she ended up driving me home, I told her I was still in love with her (yikes!), nothing happened, she cried, I cried, I puked around the corner, it was a whole thing. After that though, we did the adult thing and met up for coffee to discuss maturely (and soberly). We agreed that it’s obvious we can’t be friends right away so we took a friend-break, this happened two months ago.

We have talked sporadically since that coffee talk, never without a reason. I drunk called her once, not my proudest moment, she was very understanding though. She does wonder why I never say anything bad about her even though she broke up with me, and the truth is I just can’t. She is a good person, and shes sweet and kind, I’m not blind, I know I hold her in very high regard.

Truthfully, I’m not sure if I am entirely over her. I think about her a lot. When I hear songs, when I see cowboy boots, the usual. I developed hobbies and I talked about it. I walked around, I talk more, I took up journaling. She was my best friend though, she knew me more than myself, I knew her likewise. I’m taking small steps. I know I’m still very young, and maybe in a few years I won’t think about her this much, and it’s not the end of the world, but it is today. And it is what I think about today, and what I will think about tomorrow.

My friend group is kind of like an inner circle, with my two friends, and me, or her interchangeably. But we also have an outer circle of seven friends total. We all go out to dinners, or outings, and one of these times I know we will both be invited. I’m not opposed to it, I think I could be okay with it, but I am worried that it’ll end up like last time. I’m also kind of jealous, if she brings someone else into that outer-group, like a new boyfriend or something. I have no idea what I would do if that happened, but that’s a problem that hasn’t even happened yet.

I don’t want to leave my friend group, and I don’t want to separate them from her either. How can I manage to have a friendship with her? Even if I am still (mildly) in love with her?

TLDR; Me and my ex-gf have the same friends, and we’d like to be friends with each other eventually. How can I be friends with her?