I have no problem doing cowgirl with any other guy besides this one. What gives?

Typically my stamina in cowgirl is super high and I can go for a while, until the guy comes or I do.

The current guy I’m seeing is the only guy I get tired of riding within like 2-3 minutes. He has a big penis, but he’s not the only guy that size I’ve been with. I’ve been able to ride someone else his size for my average time

I literally have no idea where to diagnose this issue because what could possibly be different? He clearly enjoys when I’m on top and I think he performs well in MY favorite position so I just want to figure out how to be better in his favorite position