Looking for a yaoi manga:

http://www.mangago.zone/read-manga/gekai_no_okiniiri/

Ah, sorry, wrong link.
http://www.mangago.zone/read-manga/hokenshitsu_no_target/

http://www.mangago.zone/read-manga/scramble_game/
http://www.mangago.zone/read-manga/batsu_game/
Also, these aren't all sex bets, but they are all bets about some form of intimacy.

Thank you~ I enjoyed reading your recommendations~

^^