Afraid

Alright so, I’m really scared to tell my boyfriend when I’m mad/ upset/ have any negative emotions. And it’s no his fault, he’s really nice and is always validating my emotions. But in past relationships, whenever I got angry or upset I got hit because of it, or manipulated to think what I was thinking wasn’t valid. So now, whenever I do feel anger or frustration towards my boyfriend I feel really guilty. And I get scared I might loose him. What do I do? How do I validate my emotions?