Coco Chanel said something like, "When you're getting ready to go out, take off one thing.” I think it's similar with dialogue. Cut it off. Don't say too much, because then it gets to a place where it's not natural. Most people don't go on and on for sentences in real life. Also, when two characters are in a space that's emotionally raw, they can't always articulate everything. They're talking, but not saying the right things. Another thing is to never let people directly answer each other's questions if you're trying to create tension.