It doesn't take extreme memory on your part to remember to avoid that opening after the first 9 losses, or indeed the first one. There are 5-10 other reasonable options for you on the first move alone.

It doesn't take extreme memory on your friend's part either if you keep falling for the same trick. It would take extreme memory for him to have something prepared against every plausible option you could choose.

Have you considered that your cousin is also better than you tactically?

If you're losing 10 games in a row to a specific opening trap then that falls into the "fool me eight or more times" category :)