Medication talk pleases me, as I am a devoted Pharmacy Technician. Infact, I am the friend in question's pharmacy tech, and while I can't give away what she's on, she is on many, many things, and recently came off of them, which might also contribute to the issue.
Furthermore, she's also been diagnosed with borderline personality disorder, which makes things pretty weird.

I've never let someone I've been in a romantic relationship with treat me like this, after one incident in college, so it was very hard for me to even look at this friendship like that.
Anyways! I spoke to her yesterday, in between the March for Women's Rights that went down in the state capitol and the bachelorette party. I stated that I felt like she took me and my affection for her for granted, sometimes, and that I was sorry she felt like I wasn't trying, but that sometimes it felt like she was expecting the impossible out of me, like that my whole life should revolve singularly around her.
It went about as expected.
Which means that none of my feelings were valid, in her eyes. That I was just not making her a priority in my life, that I didn't care, that I was irresponsible for not keeping her updated on my social plans, that I was making her out to be a burden in my life.
And then she suggested we take a break.

So, overall, pretty much what you all suggested. In a way, I'm really sad, but I'm also really relieved because I feel like now I can go do things with friends I've really been neglecting for fear of hurting her feelings.
Thanks, everyone, for your input. It was really, really helpful.