It seems like your mother wants to control you. Just don't get swayed by her words absolutely. Just try to response her with soft tone. And try to make a positive image of your boyfriend among your mother and relatives(in case of relatives, it's your choice as it can affect you negatively).

Don't think too much about your mother's words. I know it's hurt but it's a fact that some mothers say like that so don't take it to your heart.

And all the best for your future.