Would you tell a girl that her boyfriend cheated on her with you?

I have been in love with a guy since the moment i saw him 3 years ago. it was a shit beginning, and we lost contact, but i never got over it. we became friends (sometimes lovers) again after that, our friends, etc. i found out 6 months ago that he had a girlfriend for 2 of the three years that i had known him, but he had kept it secret from me. I told him everything, how i felt and all the rest and finally told him that i needed to have him out of my life. since then, i was relieved, but empty. last weekend i ran into him, and he told me how much he missed me, that i was beautiful to him. i went home with him, delirous, it was everything that i wanted to hear. in the morning he tol me that he was not going to leave his g/f. i am so lost and so confused, i want to stand up and get angry, but i can only be at myself, i want him to not be the person that he so clearly is (i cant see it) i want to react but dont know how. im sick of holding my tounge and breath for the shiit to hit the fan.