Why is my boyfriend acting different?

Ok so we have been going out for close to a month, but he has liked me for quite a while. Well before school ended he finally started telling people about us, and he was like all over me the last two days of school. The last day he went out of his way to walk with me to my car, he said it was because this is the last walk he could have with his girlfriend. Aww :) well we text all the time, give or take a day or two, well he hasnt texted me in 2 days goin on 3. The last conversation we had he told me to promise not to go out with anyone else over the summer, he said he promised not to either. Then he said he was sad cuz he couldn't see his baby anymore. (thts me) and stuff like that. Well last night he texted me: hey beautiful and I answered: aww:) hey:) but he never replied nor has he texted me today..hmm why do u think? Should I be worried? Thanks :)