Why the fuck do you want to steal a girl? Holy crap, she is the only girl that likes the same time of music as you do and she watches anime! She must be the ONE. Just because you two have similar interest, doesn't mean you are meant to be together. Did it ever occur to you that her boyfriend may have the same interst too? You honestly have no right with getting involved in their relationship. And if you do, he has every right to beat the shit out of you. The best thing you can do is meet some other girls, because there are plenty of them out there, you just gotta look.