Left someone very important behind...

Well let's see...

My dream was taking place around some kind of zombie apocalypse. Me and this one girl were running and got on top of a train because the train was going to head to some safe zone we heard about. As the train was heading off, this other girl was running toward me. I yelled at her to grab my hand as I reached out for her but the train started to pick up speed.

The train was going over invisible tracks or something, but the girl tried jumping to reach me but she missed and fell into the water. I started screaming and I was about to go jump in and get her but the girl I was with stopped me. All I could do was sit there and watch as she started screaming for me to help. I wasn't sure what happened to her after wards.

More happened in the dream, but this is the only point at which I saw her, and this is the only thing that's important to me. I also got into some fight while trying to protect that other girl, and I was in rage about leaving the girl behind.

I know exactly who this girl was, and I've been trying to summon her in my dreams for along time now. I wanted this girl to be my Dream Guide. If I was lucid, I would have jumped in that water in a heartbeat without that other girl stopping me.

I feel like my mind is toying with me...
I've been wanting to meet this girl for so long, but when I finally meet her, I wasn't able to save her or go out and help her.

Would anyone be able to think they could interpret this dream?