There's a stalker following me on Twitter?

[Sara]

Actually i have created my twitter account last year!! and i made many friends in it!!
The thing is that i made a friend and we talked a lot! I thought i got a best friend.. when i had a break up .. she was always there for me! Now... Her behavior changed when i said to her, i can't come on Twitter regularly cause i have lots of work to do!! One day she asked me really personal questions ( things she was not supposed to ask)...i found a bit uncomfortable with it and said to her, i can't answer her that... she started to over think about it! After a few days she's still asking me about this!!
I don't feel secure at at all!! What should i do? Should i deactivate my twitter account?
But she knows where i come from!!!
Everyday she sends me messages that she's here for me, etc.. and that she'll protect me from people !! When other people talk to me there, she gets really jealous and she says to me she loves me more than them... i'm really scared of her!! She's too attached to me!!
She says she can't live without me!! i'm scared!!! :'(