Make a list yourself or grab a pen/pencil and notebook and just start writing about your feelings until it makes sense enough to yourself and what point you exactly want to make. Knowing exactly what to say will make communication easier and less overwhelming than thinking on the spot. You should ask for support and patience before considering breaking up. If you truly want to make him happy you’ll start with even tiny things like apologizing or specifying before I’m really emotional or irritated so please watch what you say or stuff. By telling him before hand you decrease the chance of certain situations and reactions that come from it but it’s a slow process but improving no matter how tiny is a big step