<human>: Give me the gist of the text in a nutshell

Hi there, just wanted to get someone else's opinion on this. I've been with my boyfriend for a little over a year now, and things are normally amazing. He is the most sensitive, loving boyfriend I've ever had, and I feel lucky to have him. Until we argue. 

Whenever we argue, he immediately gets defensive, and attacks me for my side of the argument. Big issue or small, his response is always the same "I can't believe you're saying this to me," or "I can't believe I just heard/read that." Even when I try to tactfully maintain the argument to a simple discussion level (instead of full-blown yelling), in the face of him accusing me of outrageous things (going behind his back, taking other people's sides, etc.), he still attempts to turn the argument and attack me for bringing something up with him. He accuses me of things that don't make sense, like knowing more information than I'm letting on, or trying to actually start the fight. I hate drinking with him because it just makes it worse.

Our fights end in one of two ways; he either walks away, or I concede and roll over and apologize for even bringing anything up.

But, any other time in our relationship, he is the perfect, model boyfriend. I don't get it! How can he flip-flop so quickly to being so defensive and aggressive with me? I don't understand him and I don't know what to do anymore.
<bot>: Have you ever had a partner who was so defensive/aggressively argumentative that you've been unable to speak your mind and bring up issues with your partner, for fear of a blown-out-of-proportion fight?