Do I have a right to be upset?

I have been with my fiancee for a year and a half. He proposed on Christmas last year. Today he got off his chest that he has 3 children that he never told me about. Due to circumstances at the time, he signed them over to his mother in law in 2010 after his ex wife took her own life. He hasn't seen or had contact with them since. I was so excited to be the woman to birt his first child. Now I feel as if I've been robbed of that 3 times. I have fertility issues anyway so now I feel even more inadequate. He doesn't understand why I'm so upset and can't stop crying. Any advice?