Gil describes it as an exchange. Parker is more than happy to stop gil. Remember how he wanted to stop gil and lars on Parker day 7? He mistakenly thought they were fucking in the restroom bc tora (sarcastically?) said it sounded like they were having fun, when in actuality lars was vomiting. Liz stopped him and told walter about the cockblocking bc she was concerned.
If you go to the hot springs with Parker on lars day 8 and don't play along with Tora, Parker instinctively bonks Tora because it reminded him of gil, and he talks about how he stops gil when he does stuff like this because gil asked him to.
And there's all the times Parker lectures Gil. And Gil saying he's still a virgin because of Parker.
In Anders route lars knows about the deal and thinks it's unnecessary.
These and Gil's explanation wouldn't make any sense if Parker had rejected the arrangement and wasn't trying to stop gil. He just wants it to be one sided bc he doesn't want to diet