Why are guys consistent in the beginning, but then fall back?

I was just curious...why do most guys call and text everyday in the first couple months of talking to a girl, but then they begin to fall back?

I've been seeing someone for 2 months and at the beginning he was amazing. He was in contact everyday and we saw each other frequently. Now for some reason, he isn't as in touch as before. Instead of being in contact everyday, it's every other day or every 2 days. However, we still see each other frequently and have a wonderful time in person.

So, what do you think it could be? Why are most guys like this?
Why are guys consistent in the beginning, but then fall back?
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