Welcome to the forum, Silas.
My offering to you is simply about how to regain yourself. When I break up with someone, I like to take 40 days of no-contact with them. A very wise teacher recommended this to me once, and every time I've done, I've been able to maintain a friendship. With those whom I neglected this, I am, sadly, not friends.
I am currently in a no-contact, after breaking up with one in my first, functional poly relationship.
This is not easy. It protects both of you from conversations like the one you're reeling from just now. I often write letters full of things I want to say to that person. I recently found some of those old letters, and I was extra grateful I had never said those things (now, with the perspective of years).
Three months? Love of her life? Sounds like she's got a little growing up to do herself. That seems awfully quick.
I'm sorry you're hurting; and happy that you seem to be making your way to more solid ground for yourself.