this is a cute story....ahh the happiness..
looks like in the last page Kurogane doesn't want anyone to know that he cannot drink milk, and especially doesn't want Fai to find out coz Fai will definetely make fun of him (this is what kuro whispering to Mokona), but Fai definetely quite sensitive to to what Kurogane whispering, and in the end order another 20 milk....
just my guess, and it's so funny looking at Kuro's face when hears Fai order another milks, like shock XD