Am I The One Being Selfish?

Me & my bestie have been friends from first day of college, we both are very introverted so we didn't really have a friends circle, we just had a lot of acquaintances but we didn't really need a lot of people. We were happy in our own bubble.

So recently she started dating a guy , & he is a very extroverted guy ,so her friends circle has grown... Which is fine by me to be honest but the point is , things are not the same anymore, like & I know people change, but she has changed & I feel she's being a little mean to me & taken me for granted. For instance she wants me to be there for her even when she knows I'm not free, like she had a fight with her friends from her bfs gang & was upset & wanted to go out ,I wasn't really in the mood but we went out & watched a movie , but like I understand that I'm her friend who she wants to be comforted by so I didn't think a lot about it...

Now we are third year , & the guy she's dating is in final year so ,she just explained to me that I need to be there for her whenever she needs me .

But the problem is I have flunked on one of the subjects so I have to clear the exam , but she expects me to study with her (she has been promoted to the next year & if I don't clear my make up exams than I'll fall behind my batch by a year)

But she wants to study with me for some normal tests & like she knows I'm hanging by a thread. And when I asked her to ask her new friends or bf for that. She said she couldn't do that cause her bf has his finals coming up(after 6 months, & my exam is 1 month away) . So basically she doesn't want to disturb him & his friends.

And she doesn't want to study with anyone else but me . And the thing is if we study together it's always the things, subjects she wants to study & I teach her all stuff I know she doesn't even wanna listen to what plans i have for the day.

I'm so tired like she's a good friend but like the thing is her good subjects are strong & we study together the subjects that she's weak in . But me as you can see I have flunked so I clearly am falling behind.

Like I feel like I can't deal with this stuff where I just have to pacify her after whatever goes with her other friends.

Like I'm super introverted & some people of her bfs batch have had some issues with me. And because I'm the junior in this case I really don't want to be too involved with them.

But she just does this thing where she emotionally blackmails me to do anything for her .But I really can't mess up my exams & she clearly doesn't care .

And the point is because I'm one of her friends now it doesn't matter if she has issues with me , but it bugs me because she's one of the few friends I have & honestly I been cutting her off if I feel she's being unreasonable. Am I being selfish or am I just overthinking everything.I should just sit & study ....