trying to trust

Okay so my boyfriend and I have been together just over a year. I've had a huge amount of trust in him but then he was unloyal a few months back and hasn't done sngbubg except for that one time. Anyway, he's just gotten a phone. Instagram and Snapchat. How do I stop my anxiety from spiking up? He literally just got the phone a few hours ago and just made the accounts but I'm already scared because I can't see what's Happenjng and stuff. Please help. 
Don't say I should dump him. I'm sick of those useless comments because it's not happening. I want real help on getting through this. I know he won't do anything but just scared deep down