I need help with a name vs. nickname situation. Please help!

I have a character named October. About fifteen pages in someone starts to call her Tobie. This nickname suits her so much better and that's really how I think of her. When is it okay to refer to her as Tobie in the text? Immediately after she gets the nickname?
Oh...and in my mind (not saying that it shows in the actual writing) her name change is kind of a symbol of change in her. When she meets the guys who names her that, big things happen and her life changes ALOT. She changes alot.
Oh and its a scifi-fantasy sorta. (Sorry for so many oh's)

That's perfectly fine. I've read tons of stories where the character has a full name, (like October), then a nickname is presented and that's what they're referred to as. Just make sure that it's a smooth transition. Make there be a reason she is now known as Tobie, (which is super cute by the way ), which I guess in your case would be the boyfriend.

-Carly

I say it's fine. It has great symbolism and it's like she is no longer the "October" person she used to be, she is a new and improved "Tobie".

And by the way, I love the name October! (And Tobie!)

-Tori

Carly and Tori are 100% right about it being fine.

Not only is it fine, however, it's actually encouraged. For maximum penetration, you should refer to a character exactly as the point-of-view character would. That means that if October calls herself Tobie, you'd refer to her as Tobie similarly, if she had a boyfriend "Nicholas" and she called him "Nick", so would you.

But this principle can be taken even further. If she calls her father, Dad, and her surname is Smith, you still don't refer to her father as "Mr Smith". You refer to her father as "Dad". This sort of thing enables us to become one with the characters, and helps us as readers connect to your story.

Have a great one!