How should you act when you see your ex?

Keep cool when you see your ex.Avoid trying to hide or pretend that your ex doesnt see you. If you both made eye contact, then your ex has seen you. Consider taking a minute if you can to calm yourself. Consider acknowledging the possible awkwardness of the situation when meeting your ex.

Should I tell my ex im seeing someone new?

In the end, its totally up to you to decide what the best move is. If you think it would be less upsetting for them to hear it from you, or if youre sure that youve both moved on and just want to let them know whats going on in your life as you would with any other close friend, then go for it.