i m sorry you had to go through that. just know that time heals all things and there will be a day that you wont hurt from this anymore.
i m 32 y.o, never been married but been in a simular situation as yours.
my ex of 5 years told everyone but me that he loves me but isnt in love with me. i was the boring plain jane to him, and he wanted a sexy exciting women.
i felt the same as you "how could he throw all of our history away. i knew he thought the grass was greener on the other side.
the girl we dumped me for has since left him after one year, she treated him bad, complained about how he couldnt satisfy her.
so he of course cried to me, missed our amazing sex life, and how simple i was, as oppose to some fisty girl that always cussed him out and gave him stress. but when he found out the grass isnt green i was in a full blow happy relationship with someone who thinks i am gold.
i smile as i tell this story. and one day you will also. what will he do then when he's single and you have another man raising his child.