My girlfriend's sister, help me

Good afternoons, I have a problem my sister in law doesn't know what's going on with her the truth I don't know if it's my imagination or if something really is happening and I don't know how to approach her. Let me tell you we've been having cross glances and that kind of thing, she's caught me looking at her, looking at her ass and that and doesn't say anything and I've also caught her looking at me or looking at me provocatively, also does provocative poses in front of me. I notice when we play together her nipples get hard and I don't know if it's my imagination but I'd like to know if she wants something with me, if she has a crush on me or wants to screw? Before she wasn't like that with me. Honestly I do have a crush on her I want to screw her all the way I'm dying but I don't know how to approach her what should I do? How will I know if she'll do nothing if I make a move? I saw photos of hers in thongs and that kind of thing (that was when she left Google Photos open on the PC) now I don't see her with the same eyes and I think she doesn't feel the same way about me anymore... Give me advice. I also give her likes on all the stories and photos and always raise the bar but she doesn't say anything to my sister once I even sent her a song called forget fear by drefquila (it says forget fear, I also want to eat you, although I know I shouldn't) neither did she say anything. How can I know if what I'm speculating is true and I approach her or if I should leave it alone. That girl has me crazy