Am I in the Wrong??

This is the Difference between my sister and I.

My sister is 18 years old and dating this guy that is 22 years old. My sister is a very loud, rude and really nasty in some ways. She is a very Social person out in public, sometimes I think she is to Social. She jumps from Job to Job never really getting anywhere and her Boyfriend does nothing all day he won't get a job at all. My sister dropped out of High School so she and her Boyfriend has no High School Diploma..

Me on the other hand I am 23 years old and engaged to a 23 year old guy. I am very quiet, nice, and very well mannered. I am not a very Social person, because I'm way to shy and Conservative. I have a full time job and trying to save for my Future with my Fiance. My Fiance also works to full time in Computer Technology. Me and my Fiance both Have High School Diplomas and both are looking into Colleges.

My one big problem tho is my sister is always asking me for money and trying to get me to buy her Boyfriend his Cigarettes (which is not my Responsibility) but if it actually comes down to it if she has money and I ask to borrow a little bit its always NO! I always will pay people back even if I have to do without. But my sister will not pay anyone back and I don't care to help people, but there is only so much I can do.

Another things is and I don't know if it because people feel like I got a head on my shoulders or what. My sister can get anything from people and I mean anything. Me I can't its not that easy..

What should I do? Pretty much just live my life with my Fiance and go my own way? I just feel so used.