Is something off, or is it just me?

Hey guys! I need some advice. I've been seeing my man for almost 6 months now and we've been talking about long term. He's seemed slightly distant lately, but when we're together, he makes me feel amazing and the sex just keeps getting better... but the last few times, he doesn't really say much but, "Well, that was fun." We kiss more and cuddle, but he doesn't really say anything... something just seems different. Maybe it's the relationship maturing, or something deeper... help me?!