Is it normal that i like the guy my sister's talking to ?

So there is this guy. why does every drama start like that? ha. well anyways i started to like this guy & for a month or so i thought he liked me . we play around alot and every friend of mine thought he did. well i invited him out one night. it was a group thing were me and my friends and my sister were going. well previously i had been told by one of his friends not to take the guy to seroiusly when he flirts because not everyone he flirts with he likes. and im not the type of girl to just let a guy have what they want and be done with me. So when we get ot the place he starts wanting to hug me and everything & i admit i kinda went mean because i thought, oh well he's just flirting. he doesnt like me. so as the night progressed my sister started talking to him and he ended up flirting with her and holding hands with her on the way back. so now he's "talking " with her. the next day i confronted him & he told me that he had liked me, and he wished i told him that i liked him but now he was in a commitement but if i wanted for him , when things were over he would try and talk to me. well i figured that was it it was over. But the thing is my sister is younger , she's more mooder and i decided to be upfront with her and tell her what he had said . well she took it well. but now its been some weeks and me and him have gotten to be better friends. but the thing is that he still flirts with me(he considers flirting to be being nice")and tells me i should wait for him, and he tells me his problems he'll call me instead of her to tell me. then if were standing together he'll pay more attention to me instead of her. & i cant help that i flirt back because i did like this guy. my friends tell me that it really looks like he still likes me but. i dont really know. he just might be trying to be a player. & i really dont want to hurt my sister either. what should i do?