How should I deal with bff that ditches me but at the same time not really

So my best friend now is always ditching me for other friends. I feel left out but at the same time she doesn't ditch me completely.
It's like every morning, she will hang out with the other friends and when i come, she will say hello and then ignore me and when I try to get into their conversation, they all seem to ignore me. Her other friends are my friends too but we are just not that close . Anyway, when I try to talk in that "group", they seemed to ignore me and my best friend kinda follow what they do. She only hang out with me because she has to (like there aren't anyone else) but if not, she will just go to other people and talk and left me out.
When I tell her all this and how I feel, she'll either say "ohh I'm not abandoning you, what are you talking about, you're thinking too far"
or she'll say "what? i can't socialize with other people ? "
How should I deal with this ?
Should I try to be more sociable and join the group and hope that one day they can finally "treat me well" or should I forget all of them ? But for the last option, it's kind of hard because there are a few months left before graduating so it's very hard to make new friends.
And plus, I can't loose my best friend, at least that's how I think, like we'll be always best friend and no ditch and all but for her, i have no idea. She always tell me" Oh i won't ditch you" or sth like that but her actions seem to be the opposite.
What should I do ?
Help!