DT /BF TIPS

So I want to learn how to do better at pleasing my boyfriend but he’s much thicker and longer than my last boyfriend and he keeps saying I’m using teeth but I don’t feel that I am . I need some tips on getting better at this because he’s not the best at explaining .one of my biggest issues is I don’t understand how to open my throat wider if that makes any sense … Nobody’s ever complained before but also I’ve never been with anyone his size before😩