Why did my girlfriend break up with me?

so my girlfriend broke up with me yesterday. when it first happened i honestly thought i was handling it okay. i wasn't even crying or panicking. but today feels completely different. the reality of it has hit me and the pain is overwhelming.
the hardest part is that we didn't end things because we stopped loving each other. we still love each other and we ended on good terms which somehow makes it hurt even more. all i want is for her to come back.
everything reminds me of her. when i'm sitting at dinner with my parents i catch myself thinking about how much she would have enjoyed being there with us. when my dog does something funny i immediately think about how much she would have laughed. when i'm driving i imagine her sitting beside me listening to music with me like she always did.
it's like she's woven into every part of my day and now every little moment feels empty without her.
what's also stuck in my head is something she told me before we broke up. she said she'd probably try to find someone else afterward to help her forget me. i don't understand that. maybe people cope differently but i can't imagine doing that. right now the thought of being with anyone else isn't even on my mind.
i don't know. i'm just hurting a lot more than i expected to.