Is he serious?

So I met someone on OKCupid and we had two dates. He's extremely introverted, so during the first date it was quite hard to approach him at the beginning but later I could find a place that he likes and we had a good time. The second date went really well because by that time I already knew what he likes and we could bond over that. During the dates he gave some indications that he is still interested in seeing me, and he always hugs me before we leave. But then I'm not sure whether he is serious or not (or whether he is actually into me) because he's rather cold on instant messaging, and this morning I tried to talk to him but he did not reply at all (he just saw the message), which kinda ruined my plan because I wanted to suggest something on the weekend after he replied. And no, he's not busy, because it's summer holiday and he told me he has nothing to do right now (and normally he replies instantly, but he's just cold there). So is it a sign that he's not that into me? If yes, should I back off? I'm so conflicted.TL;DR i'm dating someone, went well in real life but he's rather cold on instant messaging, so not sure if he is serious or not. Thinking of backing off if it means that he's not that into me but im conflicted