My family & boyfriend I'm torn... ugh!

My boyfriend & I are very close. We are best friends. On the other hand my family & I aren't close never really have been. But. My brother & grandma came out to visit my mom & I this weekend. My boyfriend was there. Well I got a call from my brother yesterday saying that my boyfriend is a thief (he smoked the rest of a cig that my mom was done with) & he's shady, my boyfriend barely talked at all because this is the first time I have seen my brother since Christmas. I don't understand why my brother is saying this about my boyfriend? What should I do???