Need help asap!!!! Does my GF sister like me??

Hi, so I have been with my girlfriend for 4 years now! She is decent madly in love and wouldn't do anything to jeopardise that! But I feel I should say something or warn her about her sister, her sister is older than me 2 years and is hot but also has a BF..

Now about 2 years ago she used to slap me on the *** all the time like when I was walking up the stairs and she was behind me but never in front of anyone, I used to think she was just being nice but don't know.. She also when we went out one night I ended up at the nightclub with her and her friend who I also knew as a childhood friend. But the whole night she was saying she loved me and trying to hold my hand and that, anyway we both went back and stayed at a friends and I slept on floor her on sofa she said she was cold so I got on sofa with blanket and just lay next to her ended up spooning all night. Baring in mind we are both in relationships.

Now the most recent years we have both moved away into our own homes with our partners but she is still not very far away we see them often but when our partners are both away we end up meeting up all the time and doing stuff, she also Snapchats me regularly when her BF is away putting cute filters on her and biting her lip.. Now I just want to know whether it's worth telling my GF she is like this or am I over looking this? Thanks

Honestly? If your serious about your girlfriend then you should stay away from her sister. The last thing the sister needs is something to leverage against you in order to get whatever she wants. If she isn't like that then its still wrong. Me personally, I'd never spoon with another girl if I was in a relationship. Nor would I have let it go on this long. I would've told my girlfriend whenever all of this started. I'd at least warn your girlfriend against it. Make sure you have solid proof and be prepared to take some backlash. Just imagine, if you marry this girl (who knows?) then you'll end up seeing the sister just as much. Not only that but you're becoming comfortable with her. What do you think will happen?

My advice? Lose the sister. Stay 100% faithful to your girlfriend and tell her. She deserves to know.

In any case it is best to ignore it.