It will depend on how interested the girl is in her boyfriend. Though if you become her friend and try to help her out, she will rely on you more. If you wanna date someone the best person to date would be your best friend because they would know you the most. Just don't be to clingy.
I would confront the girl or warn your boyfriend
Boyfriend.
Mostly a girl gets a boyfriend at the age 13 or 15
Ask the girl.
If a girl keep on talking about her ex-boyfriend to you that means she still loves him!
If he wants to marry another girl he's not your boyfriend.
Then she has to choose you or her boyfriend.
If she has a boyfriend, leave her alone.
That she isn't ready to have a boyfriend yet or she is to busy for a boyfriend.
You don't.
Get a boyfriend and love him..
if i where you i would tell the girl that likes that boy that he has a girlfriend.that is what i would do.