Boyfriend going to parties

ally
So my boyfriend and I have been together just over a year now and he's going to parties and not inviting me to go. I understand that he might need his space from time to time. 
But there's this girl he's close to, had a crush on her in the past and she's really flirtatious. They go to the same school, he doesn't let me check his phone even when he checks mine... I feel like he might be hiding something? Or am I over reacting?? 🙈