1) To start with, change your Facebook password and your computer login password immediately. Make sure the new password is strong and difficult to crack- in particular, dont use names, dates etc. that your ex might guess.
2) That guy typed in your IP address?? Do you have a static IP? PCs with static IPs are easy targets. You can set your computer to always set "Obtain an IP address automatically".
3) Check your computer for trojans. Free online Trojan Scanner - Scan your system for Trojans
4) Dont click on suspicious/unknown email attachments.
5) If there are shared drives on your computer, turn off sharing or make sure it requires a password.
6) Make sure the firewall is not turned off as Liquidsnake has already talked about. You can also try a different firewall such as comodo or zonealarm.