My best friend betrayed me

So we had plans to go trick or treating, and they said they would tell me where they'd get dropped of at.  They had a sleepover but their mom said no. I was super bummed about it, and I told them that. 

I asked them if were going to the downtown trick or treating event, and they said yes.

We met up, and I let them walk around w/o me bc I'd already gone to every station. I found them a bit later and they told me they were going home. One of them, A, even gave me a side-hug and told me she wanted to go with me trick or treating. 

I go trick or treating, and see them together laughing, having a great time. Later, I texted A, and she told me that she can't have fun around me, and that I'm depressing. 

I'm really hurt and I don't want to friends with them anymore.