Is it time to let go of this friendship?

I have a friend who I talk to a lot. I consider her a very close friend. We met in jr high, and now we’re both 19. We used to talk a lot all the time about anything and comfort each other when any of us were sad.. but for 2 years now she’s been different like she doesn’t care for me anymore. When I send her messages a lot of the time she’ll leave me on read or reply ‘oh’ or sometimes ‘LOL’. Even when it’s sometimes not even funny.. And when she’s sad she comes to talk to me and I try my best to make her happy because I care a lot about her, I talk to her for hours. But when I’m sad I tell her about it and she literally will just send ‘oh’ or ‘:(‘. That’s it.

I feel like I’m just tossed aside and that I’m just a burden to her, but I haven’t really let go because honestly I don’t have any friends as close as her. I have like 4 other friends and they’re not close or best friends. She’s someone I used to tell everything to but now it feels like she doesn’t care about me.

I have confronted her about this twice and she’s said ‘I’m sorry you feel that way :( I do care about you.’ but it really doesn’t seem like it. I don’t wanna seem like a whining baby but I just wish she cared about our friendship as much as I do.