A fellow player believes that there is a contradiction in the rules of The Multiverse. "You can't ignore another players actions" vs. "Your reality can have his actions not ever having occurred". I believe that this is not a contradiction, but how can this be?
First, we must make sure to understand three things;
A single player writing for a single character can have one or more universes associated with this character. New universes can be created for any number of reasons, including the player changing their mind about the character's history or direction. For the sake of simplicity, let's start with the assumption that every character has but one universe with a linear history.
When a second player is introduced, the newly introduced universe may or may not be congruent with the first player's, and conceptually a third universe (called a multiverse, with a very importantly lowercase "m") is created. The player is required to roleplay along with whatever is happening in that new multiverse, but is not required to incorporate what happens there in their own personal universe.
When subsequent players are added, the number of multiverses increases factorially. The set of all possible multiverses is the very premise of the roleplay in question, The Multiverse (uppercase "M", because this is a proper noun), which is defined as a collaborative fiction.
This third concept is very important, because it is the crux of the issue. The very spirit of The Multiverse is such that we wouldn't have a roleplay without our willingness to collaborate, and moreover to offer our creations up for shaping by the often unexpected forces of other players' universes.
Your universe might not incorporate certain events as having happened, but the universe in which they are "ignored" is outside of the Multiverse, which is again defined as the set of all possible multiverses. That's the firm line drawn by the rules.
Now, as for the trust that the Game Master has in your participation, it is exactly the same type of trust that each player must exhibit for each of his fellow players: if we didn't count other players' actions as meaningful and having lasting impact on our own characters, we wouldn't have much of a roleplay, now would we?