what would you do in this situation? Sparring question

I'm sparring a kid that has a 15 pound weight advantage, I know weight shouldn't effect sparring but we spar pretty hard, he knows I'm newer so he doesn't go 100% but he always walks me down, I will throw a 4-6 punch combo then retreat but that just murders my energy because i end up running away until I see a shot, I throw my jab while I back up and I'll usually lunge foreword when I know he can't hit me to throw the combos, I end up throwing the faster punches in 4-6 combos but he throws the cleaner single shots and the 1-2 or 1-1-2. How can I use my speed to my advantage?

 

Checked some vids out of him, That was pretty impressive! I do find myself backing up and going on the defense once I start getting hit. I'm going to work on throwing my combos while moving to the side. Thanks for the helpful advice!