What your advice on this

For me and my boyfriend's first started dating he would sometimes message his ex-girlfriend and I had finally told him to stop and after like the 3rd or 4th time he did but I still get really mad when he looked her up on Facebook or unblock her now is that normal like am I allowed to get mad or am I just simply jealous and should just not worry about it and when they were messaging it wasn't like anything dirty it was more like how are you doing but I don't believe that you should be friends with your ex when you're in a relationship agreed or not agreed. I know there's like many questions in this thing but whatever your advice is on this please help thank you no judgement