Confused love

My boyfriend and I have been dating for nearly a year now and have never had a problem. But recently I'm starting to feel like I'm just bothering him. We live about three hours drive away from eachother so only see eachother every 3rd weekend or so. He's extremely chill about everything and rarely shows much emotion. When we're together we're always happy and its perfect but when we're apart i feel like i bother him occasionally and more often so, his replies seem to take alot longer and the messages seem less enthusiastic. I dont know if this is just him being a guy or just being more casual in the relationship or if he's getting tired of it. I need help and whether or not i should talk to him about it..