Adventuring group yaoi manga

This is just one chapter in something that had several. I think there was a main story and this was either a parallel universe or it was just as extra.

Anyway, there are... four guys or so, and they're an adventuring party on a quest. When they enter the enemy stronghold, they find one of his main subordinates has laid a trap, and has locked all magic in place. The fighter, not being magical, vaults up to where the enemy mage is standing and attacks (?) him. When he wins he doesn't kill him, but instead has sex with the mage. This continues for a while, with his party members still frozen in the room. The last panel has him introducing the mage to the others, saying, "This is (name). He wants to help us now." While the mage cuddles close, apparently changing sides.