He says bentornato which means "welcome back" in Italian. He says this to Germany because he believes that Germany is Holy Roman Empire and is welcoming him back (Italy thought Holy Roman Empire died in war). In page 9, Italy messes up Germany's hair which makes him resemble Holy Roman Empire and so Italy believes Germany is just Holy Roman Empire with amnesia (Hetalia fans would know what I'm talking about).
@CapriciousUke I'm sorry, it has nothing so elaborate as that. This story her is only the smexy part of the story. If you ready the whole thing here, you'll understand: http://www.mangago.zone/read-manga/hetalia_dj_aru_otoko_no_haiboku/
Why does he start crying on page 28?