thanks everyone - I probably just needed to let off steam and hear that i'm not mad for feeling hurt about this. Of course the basic fact of the matter is that someone i liked chose someone else over me and there's no getting around that that hurts, and i'm not wanting to try and convert him.
Still i wonder about how to negotiate the way monogamy, normalised as it is, is sometimes used as a way of side-stepping the real issues.
If he is monogamous then there really is nothing else to say therefore it is self explanantory. He wants one person who wants one person. That could be just the way it is.
All very well. But then one would expect him to have ended things with me before getting involved with someone else, or to have asked me if i was willing to consider monogamy and thus reached a mutual agreement about parting ways or not. (I have not been seeing anyone else during the the year we've been seeing each other, by the way, and he knews that.)
I know life is seldom so tidy but the reality of the matter is that he met someone who he likes more and who is more practical for him (we live on different continents) and he could have explained that and confronted it instead of dodging those feelings by hiding behind a word that explained very little.
Quite frankly i also think its dodgy to end a relationship from this stand-point because it produces a certain uni-lateralism - any pain he might have felt is lost in a fog of new love and any pain i feel is simply reduced to the unavoidable by-product of clearing the way for his new relationship. Anyway again the world is not tidy and i've not always understood how to be considerate to others, so i will find a way to forgive him.
But I suppose what i am looking for those few pithy words that would stand a chance of breaking down the wall that word 'monogamy' throws up so that at least we are able to deal with a concrete, specific situation. God forbid that i should ever need them again.