I'm feeling guilty about something and could use some input. My boyfriend of almost a year's younger brother (who is actually a year older than me) struggles with depression and anxiety. One way his anxiety manifests itself is that he is afraid to take the bus. I have anxiety too, not judging, whatever.
However, the brother relies on his parents (still lives at home) to drive him to a sports practice 2-3x a week since he does not drive either. When they are unavailable, the duty falls to my boyfriend. When he's unavailable, the brother often asks the boyfriend to ask me if I will do it. Now, I don't mind doing favours, but the brother lives about 15 minutes away from where we live, and then it's another 15 minutes to drive him to the practice, and then another 15 back to my apartment. 2.5 hours later, I have to pick him up at practice and drop him at home (and those times are in minimal traffic - it's at least doubled during rush hour). I HATE doing this - my boyfriend's brother is nice enough but it's inconvenient, my car is a piece of shit, and it takes a lot of gas. There have been promises of gas money before, but I've never actually received any.
Just to clarify, my boyfriend understands if I say no, but still asks me to do it when he can't.
So... am I justified in saying no to doing this? I just got asked to do it this evening and I said no - I'm tired, I had a long week, I want to relax before my birthday tomorrow (

). But, I feel like I'm letting everyone in my boyfriend's family down when I say no.