I just found out that a bunch of my personal information is on the ineternet, There are 2 people who would have done this. My ex, or my roommate. How can i trace it back to either one of them?
First I'd ask the site owner(s) to take down the information. If it's personal, they should comply. It's likely that the information could be copied and put on several sites.
Otherwise, you'd need to find where the information was originally posted. Once found, you could ask nicely to see if the site admin will give you the IP address from where the information came. If you get the IP, do an IP Address Lookup. This will give you an idea, but not 100% pinpoint the location.
IMO, it's best to get local law enforcement involved or possibly an attorney if your character is being slandered. Take screenshots of the information that include the URL of the site in the address bar.