My boyfriend lost it and hit me over a joke?

we were enjoying our time and I made a joke about me kissing his close friend

without any word he slapped me and got up leaving the house

after few hours he sent me a text saying he is sorry and he couldn't handle hearing that

I feel sad and hurt especially that I have always been loyal to him and it is the first time he do that to me after dating for 3 years

now I feel afraid of him and I fear it repeating I do not know what to do

My boyfriend lost it and hit me over a joke?
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