Does she wanna leave things open in the future for us?

Alright, so I've known this girl since April and I always had a crush on her and always thought she had a crush on me as well. Well as time went on it looks like I was right as she has done things like take my phone and write "Hi Joe <3" on my wallpaper and then every time she see's me she checks to see if I still have it while she thinks I'm not paying attention. She has always done things when we have went out to eat like steal my burrito when I got up and had it hidden in her purse. She always talks to me about ANYTHING and asks a lot of questions? The problem? She has a boyfriend who she has been with for 9 months now. She has been with the guy since I've known her, I know she's not the type of girl to ever cheat on her boyfriend so why is she flirting with me? Do you think she's trying to keep me open as a possible boyfriend in the future if things between her and her guy were to fall through?