Decoding guys behaviour?

From the first time we started texting he was funny and curious to get to know me on the First date we clicked. We got on so well we chatted from 7 til 11pm. Even shared a first kiss. He texted constantly that night and the following day.
Second date we went to eat and then the cinema, we were actually incredibly naughty. But still very much into each other. Still texting nonstop.
Third date we had dinner and spent the night together. We did things but he couldn't fully perform.
He was happy to check in with me when we went to work.
And just kept showing a keen interest.
He seemed a little quieter than usual.
Fourth date he nearly cancelled, he was supposed to be staying over for the night and cooking, in the end he did. But this time he seemed to have anxiety because at some point he said he felt sick.
He had to use the bathroom and seemed ok the rest of the night.
Slowly his texts have been reducing, the morning texts are no longer consistent, they're not always with kisses, sometimes he can nearly go the whole day without making contact.
Even his messages in the evening are a little hit and miss.
He hasn't made plans to meet again nor any suggestion but he claims to be incredibly fatigued.

I feel like I'm being fading out.
But everytime I think he won't bother again he does and sends a picture of his breakfast that he's preparing...

The mixed signals are confusing.
Decoding guys behaviour?
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