I think my boyfriend is talking to someone else, how do I approach him about it?

So over the past few days I've been feeling like my boyfriend is speaking to someone else; he lives 2 hours away from me so I only get to see him every other weekend. As soon as he woke up he'd used to text me straight away, now he'll go on facebook and not text me for ages. He's really hard to get hold of, I'll try and call him and he just won't answer. Also I think he's got a new snapchat because he hasn't been active on that for a couple of days now. I want to talk to him about it but I don't know what to say. Please help!