<human>: I am still friends with my ex because we like all the same things, have the same friends, go to the same university, etc. He broke up with me over a year ago. 

Here is the deal, a big problem in our relationship is that he got drunk one night early one and told me he had doubts about our relationship because he had a crush on this mutual friend. The ensuing jealousy and insecurity caused about half of our relationship problems. 

When we broke up, this female friend told me that my ex was hitting on her and that I should talk to him about it because it made her uncomfortable. I considered this to be an insult from her because she also proceeded to talk about how annoying he was behind his back. I told my ex about it because I felt I owed him that if we were to be friends. He was upset with her and they didn't talk for a while.

Fast forward to now. He tells me they have been talking and now that she broke up with her bf, he asked her out and figured he should "warn me". I am upset because I consider it a breach of friendship etiquette to not ask a friend before dating their ex. This girl confided in me when this exact same scenario happened to her a couple years ago, but now she is doing it to me. I know myself and it will cause me too much pain to see their relationship all over facebook and in person so I'm taking steps to avoid this. I unfriended both of them on facebook and canceled all plans which would have both of them in attendance. They seem to think my reaction is unreasonable. I'm just curious as to reddit's opinion on whether my reaction is excessive.

Can you provide a brief rundown of the text in within 3 sentences?
<bot>: Friend and ex want to go out. Friend didn't talk to me about it first. I ended my friendship with both of them. Am I overreacting?