Guy's Behavior

Why has he suddenly gone quiet on me?

So I met this guy at a party last Saturday, and we really hit it off. We've been messaging each other ever since then, but usually only once a day, as he's been on really long days at work. And he asked if I wanted to meet him soon, and I said I'd love to! But the past day or two, I've sent him messages that he hasn't really replied to - by which I mean, he'll completely start afresh with messaging the next day, and not answer any of my questions etc. And then last night, he didn't reply at all until I sent him another message this morning asking when I could see him. We'd planned to do so this weekend because his step mum and dad live across the road from me, so he spends weekends with them. But this morning, when he got back to me, he said he wasn't coming up today because it was raining, and tomorrow he was going bike riding up some hills (fair enough), but I could see him Sunday evening. All wink emoticons had stopped and he seemed to have gone a bit flat. So we eventually agreed to go for a walk (because it was completely up to me what we wanted to do, apparently) Sunday evening, but I'm worried he doesn't want to, because he seems to have cooled off. So, has he gone off me? Just not sure if I like him back? Maybe I caught him on a bad day? What do you all think? Or is it because he's older than me (18) and so not quite as excited about dating as me?
Why has he suddenly gone quiet on me?
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