Help! I think my Guppy's dorsal fin is tearing away.

Like I said in the title, I think my Guppy's dorsal fin is tearing away. I noticed it a couple of weeks ago, my Guppy was fine when I first got him, but after a while, his fin seemed to be coming loose, I've been keeping an eye on it since, and while it's not easy to tell, I think it might have slightly worsened.

Anyway, what do you all think, is something wrong with my Guppy or is everything okay?

 

Are there other fish in the tank? They might be nibbling at his fin or something like that.

 

Yes. Including the one with the torn fin, I have two Guppys, one harlequin rasbora, one panda cory, and one albino cory, but I only got the second Guppy and both corys after I noticed the first Guppy's fin was tearing, and the harlequin has never shown any hostility, so I really don't think that's the case. In fact, out of all of my fish, the only one I've ever seen nipping at the others is in fact the same Guppy whose fin is tearing.

I also used to have a pineapple swordtail, but it died a while ago.

 

Hm, then I don't know. Pictures would probably be helpful, so that someone with more experience than me can help us out.
Although, aren't the Rasboras schooling fish? It could be lonely or bored and decided to fin nip. I don't really know though.

 

I'll try to get some photos up later.