Why has my boy friend's behavior changed for the worse towards me?

we have been together for almost 3 years and we love each other very much... i mean that how it is to me... but lately we are constantly fighting and we hardly ever talk... he is always angry with me and says the most hurtful things... he now days always answers rudely or just avoids talking to me... and when i confront him he shouts at me and after the whole thing blows over he tells me he loves me a lot but i have changed... but as far as i know i still behave the same... in fact... all these problems have cropped up since last 6 months... i am at my wit's end to fix this... i have tried everything from trying to have a talk to shouting at him , to pleading with him, and even emotional blackmail... i only know this much that he loves me a lot... but i can't understand his behavior... please help...