Call your ex. If this is uncomfortable, write him a letter or ask a friend to speak with him.

Tell him how his jealousy is impacting you, and how it makes you feel.

Be honest. Make sure he knows you are not interested in getting back together, and need him to cool down if he wants to even be able to maintain a friendship.

If you and your ex have mutual friends, ask those friends to speak with him about his behavior.

Find ways to distance yourself from your ex, particularly if he continues to express jealousy after you have told him his attitude is a problem.

Include your friends in this decision. Tell them what you're doing, and why. Ask for their help in maintaining a distance between you and your ex.

Alter your routines to avoid your ex, if necessary. Walk a different way to school, eat elsewhere and leave no room for doubt about your actions.