Jealousy probs 😖

So my boyfriend has had sex with over 15 different girls!! When I first found out I reacted so bad to it. It hurt my feelings knowing i was the 16 one. He was naming so many girl I knew i got so furious with him and went upstairs. When ever we have little argument and I always bring up his past I don't like doing it but it gets me so mad. Am I supposed to get this jealous? I mean he's mine and I plan on staying with him for a long time. How do I stop getting jealous and mad over his past?Â