I'm going to tell my boyfriend not to eat our groceries so fast
Why don't you want him to eat the groceries so fast?
The groceries meant for the whole week should not be consumed so fast.
I understand how you feel, but if your boyfriend bought the groceries then he can eat them if he likes. It's not right to try to restrict his food choices.
My boyfriend needs to listen to me and I don't like his plate manners
I don't think it's right for you to make your boyfriend listen to you, as that can come off as very controlling. In addition, if you don't like the way he eats, then you should bring it up to him in a polite way.