Brother keeps beating the absolute **** outta me during light spar

So, for context, I'm still a kid, and he's 18. We do boxing with a trainer thrice a week, and I do strength training/go for runs 3 times a week. He's about 6'2 and I'm 5'8. He absolutely shits on me every time we spar. If I dare to land even a single punch on him, he gets mad, and beats the hell out of me (even if we're in light sparring). The trainer does separate us after a point, but it's gotten to the point where I'm scared to box. I used to love watching the sport, but half a year of constant beatdowns and temporary blindness have removed my love for boxing. I need some way to get around this. (My family cannot afford to pay for separate sessions or for a gym membership).
Please, help, someone? How do I get around the bigger guys?
P.S my age is incorrect in my profile because it wasn't allowing me to make one with my correct age.