I mean, I can understand this in the context of conflict.

But someone left me after 4 months, saying she wasn't ready for a serious relationship. She also told me she was in love with me, had never felt closer to a partner, that I was her best friend in the city, and that she expected to be very sad for a long, long time.

And there was no real conflict. She needed a lot of space (which I gave her), and she seemed to have anxiety about the idea of "being in a relationship."

I just don't understand pushing someone away when things are going smoothly, and that is your primary source of intimacy. This relationship was my healthiest yet, so I don't feel like I contributed to pushing her away.

Why would someone choose to feel sad and alone over being with someone they love who loves them? This is so far away from the way my brain and heart works that I don't understand.