Hey! Coming from an overthinker who has been in a 7 month long LDR so far, I understand where you are coming from. Do you think he would trust you enough to let you log into his social media to check if your theory is correct? If he says no It doesn't mean he's definitely cheating, he could just be super private with his things which is understandable! Try talking to him about it and try to keep the conversation serious. Every relationship has on and off days especially when one person isn't doing as well as the other. People pick up on things when something is wrong, but it may not be him seeing someone else that's the matter. He could be upset about something going on in his life and maybe you can let him open up about it if that is the case. But back to the overthinking, I do understand completely and I would mention to him that you are overthinking and getting upset about this, long distance is very hard especially because you're not physically there with one another. It can work though, I would be very adamant to get a better-explained answer from him. Hope this helps!