How does he out-sex the sex worker? Everytime they do the deed, seol beom gets eaten up.

Well for staters he technically isn't a sex worker. Whute bear is a sex streamer, but as far as I understand from his thoughts, he was a virgin before sleeping with Snake. Yes he did masturbate and played with his ass, but seems he never had intercourse with anyone. ╮(￣▽￣)╭