I only read the first post and no one elses, so sorry if this a repeat of what's been said.

DO NOT LET ANYONE LIVE THERE WHO IS NOT ON THE LEASE. Clear enough for you? I've had "Friends" need somewhere to stay for a month or 2 and it turns out to be you, the lease holder getting shitted on.

Split the bills up evenly.. I.e had the power bill in your name, the gas in another roommates, and the cable, etc in you GF's name. Then just split them up. I say this way because if someone doesn't have money to pay you for YOUR billed name, you should cover it.

It is sooo important to look out for you own credit. I've rebuilt mine TWICE because of roommates and not double checking myself with lease holders.

Hope you can use this.