friends toi depended on me

i have this one friend and we've been friends for 6 years now, we're very close and talk every day. i like being friends with her but the problem is -shes too dependent on me to the point where she cant really do anything without me or go a few hours without constantly texting me. i mean i kind of get it because she does have social anxiety so she's too scared to look for more friends, im also her only friend bc of that reason. i even offered that i would help her, i would find friends along with her and approach ppl while she could be by my side, but still no. she says im the only friend she needs, which is nice, however i feel like she doesnt give me space bc shes the type of person that NEEDS to share ab her day with someone or mention every single detail that happens to her that day, so often i just leave her on delivered bc 1. its really too many messages every day and 2. i have bad depression and tend to really isolate myself during these depressive episodes. it leaves me feeling guilty for not paying enough attention to her, she becomes sad when i dont respond. i respond to her like every 2 hours, i try to but its a lot for me. she doesnt really go out unless its with me.

but what really concerns me is that im not a good influence. due to my depression i have missed a lot of my classes, basically im gonna fail this year. so im planning on just leaving this school and for next year having online school, that way i would have enough time to work on myself and also on school. but, because i was so absent at school (we go to school together), she started skipping too. she doesnt want to be at school alone which is totally understandable, however it really makes me feel really guilty. i have thought of leaving her bc i felt so bad of constantly disappointing her by not giving her attention all the time - i think a different person who's more clingy like her would make a better friend for her specifically. but just leaving her alone for one day is enough to make her have a whole breakdown so im not sure how'd she handle me leaving.

another thing i also kind of feel used by her, im her number 1 emotional support, aleays ready to hear or comfort her. i dont really mind that but when its me who needs to vent just a little she changes the topic immediately and the focus is back on her. and financially used by her as well. im the kind of person who will buy u a meal if u dont have money and wont expect u to pay back, so she really uses that. again, i wpuldnt really mind it if she at least thanked me or said please, when we're in a store she just chooses whatever food she wants, without asking me to pay for her, and then at the cashier she gives me the stuff that she picked so i could pay for all that. its not an insane amount of money but doing that almost every day its a lot. so by the end i just feel used. i even told her to at least thank me or something but she only does when i tell her to, never by herself. i know i should be more assertive in this situation but i feel bad to say no with the food as she doesnt have a lot of money and doesnt eat unless someone buys her her favorite food bc shes a picky eater.

soo not sure what to do with her bc if i left she would probably feel miserable:( and i really enjoy her company and everything but its just..too much