Questions, questions, answers?, how do you "fall out of love" so quickly? Options

[IamRad]

So for 6 amazing months with my boyfriend, nothing went wrong..we never got into any arguments, nothing like that. He was like my best friend, we laughed, talked, joked around etc.
Then May rolled around, and usually we would hang out alone once a week, so as usual i asked him to come over...as the weeks went by he kept making excuses as to why he couldnt come.
Well, the day before our 6 month anniversary, i invite him over, he says yes...and i get all excited and such, because i hadnt been alone with him for a month.
Turns out, he was coming over to break up with me Now of course im in total shock, and i can hardly speak, but i manage to ask him "why?"
He said he just hasnt felt right lately, and of course he gives me the "its not you its me" line...

My question?
How do you go from being so "inlove" as he told me many times....to just gradually losing that feeling?

Now the thing is, im stuck with all these questions i want to ask him, but i have no way of contacting him since its summer. The fact that i actually fell inlove with him, and he's just been taken away from me kills...

&& another thing, if i ever do get to speak to him online or something, how do i even begin to have a conversation with him about our breakup? we will eventually have to have it, seeing as he still wants to be "really good friends"