I want alone time with him!!!

Ugh!!! I'm off from work today, my boyfriend got out at 5 we have the rest of the night free. We start making plans to go to the movies, eat, im getting so happy and excited AND then he says 'my brother is with me again.' this happened the last couple of months!! We literally can't be out alone on the weekend because his brother tags along EVERYWHERE now. I'm so annoyed! I don't want to be a bitch and tell him anything because it's his brother and I love the kid like my own brother but he's 15 he has friends and family his age who can hang out with him at least one night!! Seriously like ugh!!!