Jealous Girlfriend ?!

So my boyfriend sent me a snapchat but it wasn't meant to be sent to me but to another girl. It just said that he has uni and says when he's free. At first I thought it was meant to be sent to his guy friend so I didn't care but he told me that the girl was cut because he was suppose to visit him and talk because his been busy. I kinda felt like jealous and didn't want him to go visit her but I didn't reply to him cause I was kinda upset. How do I not become so jealous because there's nothing wrong with him having a friend that's a girl. And I feel like I don't trust him but it's all me cause I just have issues trusting anyone really. So do you girls have any tips on how not be jealous ? Cause I don't want to be overprotective or be that girl who won't let their boyfriend have friends that are girls ?! This is my first time being in a serious relationship so yeah please help !