Am I overreacting?

So, my boyfriend John and I have been together for 3 years. Recently, he had become friends with his ex that had caused some problems in our relationship before. She had posted a picture of her breasts with the nipples starred out on Facebook, and he liked it. So, I decided to say something about it and we got into a fight, where I remarked that I didn't like that he talked to her or looked at pics of her like that because she should be in the past. Now, he's mad at me and claiming that I'm overreacting and telling him what to do. I've been cheated on before by my ex husband, and despite the length of my relationship with John, I still have some trust issues.