things change... people change, we can grow apart... maybe you were too close that you suffocated your bff... 

it's not your fault nor it's his fault... we all need to breath at times... try to let go for a while and search for new friends.. maybe you'll find that someone else will understand you much better than he did...

i know it's hard and that you REALLY want to find at least 1 reason to convince you why this is happening... i know a part of you wants to fix things, and doesn't want to let go... (been there...) but you can't really change anything if he made up his mind.. as much as you can still be friends but not as close as you were...

good luck :-)