How do i answer him when we quarrel?

ok. my bf have been quarrelling with me for the past few days because i tend to kep quiet and think a lot before i answer. for a simple answer like "dear, dont think too much ok?" or "send my regards to your grandma" just takes me a long time to voice out. i dont know why i am like that too. i have been tryin to change and just say whatever is on my mind. but somehow i just keep thinking about whether he will be angry if i said this or will i say the wrong thing. now, he wants me to explain why it is so hard for me to say such simple things. how do i answer him? i really dont know myself too. i explained that i tend to think much more and i will only answer when i confirm that it wont make him angry. but he says when i speak like that it means i dont treat him like my bf. how do i solve this?