VERY VERY rare situation! Ruling needed badly!

[reedchar]

While playing a round of Munchkin Marvel Edition, Player A was level 9 and Player B was level 7. Player A (9) was currently losing to a higher leveled monster, and player B(7) decided he was going to help Player A(9) defeat the monster, which if no other cards were played, would have ended the game.

Player B (7) argued that his objective was to force other players to play hand cards that would increase the monsters level, thus forcing them to lose hand cards that could be used on Player B (7) at later stages of the game. Player B(7) had good information that other players had enough hand cards to help the monster, but was not 100% sure.

A different player argued that this cannot be done simply because Player B(7) is in the action of helping Player A(9) win the game, and it is counter intuitive to the objective of the game (to win and to have other players lose). This player argued that all players had an obligation to stop any level 9 players who were about to win the game.

Player B(7) argues that his intent was not to have the other player win the game, but to force other players to waste cards that wouldn't be used on him in the future.

Does Player B(7) not have an obligation to try and stop a level 9 player from winning? Or can Player B(7) help a level 9 player get to the winning level, forcing all other players at the table to use monster-helping cards?

I know this is a lot of text, but what is the ruling on this?