Internet Battle Advice!

I am a full time student in college and moved in with two of my friends. My friend who already graduated college had her laptop (that her parents bought her) . She noticed the one that I had (old and slow!) so she offered to let me use the laptop for school. So my boyfriend moves in and he and I decide we want internet. (He mainly wanted it for his XBOX LIVE, and so I could also use it for school) So I set up the net so I could use it on her laptop. Both my boyfriend and I pay for the internet. My two roommates don’t. (They pay for cable they have in their room.) My roommate (that didn’t go to college) is always asking to use the computer for myspace or whatnot. She will make up things like needing to make a resume or looking for jobs. If the roommate that let me use the laptop can use her laptop anytime for anything but the internet because we pay. We have yet to confront each other so I need advice! Is it right for me to let her use the internet just because I am using her laptop?