Why is he acting silly all a sudden?

there's this guy I'm kind of seeing, and he's told me how he feels about me. We've hung out so many times, only made out but never had sex. We had our first kiss on our seventh date, and nothing else happened. We're very fond of each other, and have been vulnerable to each other already. He told me yesterday he can't wait to "make love to me", and when I accused him of only wanting to sleep with me, he got hurt, and said we should stay platonic cause he doesn't want to lose me over something silly. We got over it, and decided not to be platonic, and throughout the day he seemed fine, now he's acting silly, and being very childish, and almost guarded. What made him start acting differently.
Why is he acting silly all a sudden?
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