Trust Issues

So me and my boyfriend are in a LDR and we see each other up to 2 times a month and it'll be 11 months on the 26th. I'm really happy with him but one thing that gets me is I have terrible trust issues. He's not big into social media so he only has Twitter and snapchat but his snapchat score is constantly rising but I don't want to be that crazy girlfriend that overthinks and gets upset for no reason. I've mentioned it to him before and he's promised that I'm the only one and I've seen everything on his phone but idk what to do. Any suggestions?