Are these people Sociopaths?

How is it possible for someone to treat another person this way?

I was dating a girl, and everything between us was great at first. Then she went through some stuff in her personal life and started withdrawing. Because I didn't understand avoidant attachment at the time, I just showed up the way I knew how. I'd send her sweet messages even when she wasn't responding: “Hey, thinking about you,” “Hope you're okay,” etc. Nothing demanding. I genuinely thought I was supporting someone I cared about.

She ignored almost everything.

Then, completely by chance, I ran into her at a restaurant. She's out living a full life while ignoring someone who genuinely cares about her.

Here's the part that really messes with me: at the beginning, before I became emotionally invested, I repeatedly checked in with her about us. I asked if she was comfortable with the direction the relationship was going and whether she genuinely wanted to keep seeing me. Every time, she reassured me that she did.

Then, over the course of about three weeks, she withdrew almost completely and eventually broke up with me.

Meanwhile, she's going out, dancing, playing volleyball, seeing people and apparently continuing with her life. I'm sitting at home literally crying over what happened and trying to understand how someone can seemingly detach that quickly from a person they said they cared about.

I know calling avoidant people “monsters” isn't fair, and I'm writing this from a place of being extremely hurt. But right now, that's genuinely what this feels like from the other side. It feels incredibly cruel to be reassured until you're emotionally invested, only to have that person withdraw without really communicating what changed.

For people with avoidant attachment who have been on the other side of this: what is actually happening internally when you withdraw like this? Do you still care? Do you miss the person? Do you feel the loss later? Or have you genuinely detached and moved on while the other person is still trying to understand what happened?