You have several choices for situations in which one character interrupts another.
Words on the page
What you see vs. what you say
Eric Heisserer offers a good example of why you need to make sure to read dialogue aloud.
We love our pastor’s wives
A helpful tutorial on apostrophes.
Cut a character, save a scene
Last night, I struggled with a scene that went on too long without really accomplishing its aims. The solution ended up being pretty simple: get rid of a character.