What do guys mean when they say "awww ".?

That either means whatever you said was cute because as you said he has already told you once that he misses you and now he thinks that it's cute that you agree with him on that or it means that he's not sure what to answer you and was just replying something just for the sake of replying. But I think it maybe more of the first one because he has already said that he misses you. So it is best that you guys meet up and talk to each other out so that you can finally decide if you want to hook up again or leave each other forever. Best luck! :