Originally Posted by MonoVCPHG
It sounds like your boyfriend has a bad case of "give and inch, take a mile". If he demands everything at once and offers you an ultimatum, I'd say he needs to look at how committed he is to your relationship. If he feels that trapped he should move on and stop laying guilt trips on you. Sorry to sound negative but this kind of thing reeks of selfishness and childish impatience.
I am someone who gets rather annoyed with people trying to corner me 'their way'. However, if you are invested in someone, then you give people the time they need to adjust in the beginning. You do not seem to be asking anything unreasonable, while he seems to want it 'all' now. Maybe he needs to see it from another point of view.
Also,..are you sure you both have the same definition for the terms you are using ? What you define as a 'open relationship'...is also what he defines ?