Disliking SO's family members

I can't stand my boyfriend's younger brother. He's entitled, immature, lazy, and just overall the complete opposite of my boyfriend! My boyfriend is constantly having to speak to people for him, offer to help him financially, do things he or we don't want to do because his brother throws a tantrum and so much more. Anytime I say something in regards to this, he says "Family first. I'll always choose family before you." Which I understand but also take offensively because I've been there for him when his brother wasn't and I do so much for him! So I have to keep my mouth shut. I got his brother a job and make sure he works often and he still screws me over and acts like he doesn't like me. Any advice? 😕