As frustraing as it sounds, don't approach your boyfriend with frustration at first. I certainly don't think you have to tolerate your boyfriend's brother being with you and acting like a jerk all the time but you usually get people to listen more when approached in a conversational manner rather than an explosive, upset one. Propose that you take your son to the zoo (or anywhere) next week and for it to just be the three of you. If you don't go out alone often then I don't see this being a problem. As far as your boyfriend's brother being a pig, there isn't much you can change about that but you can express how you don't want him to set a poor example for your son.