Relationships in Adulthood

My fiancé is still friends with a girl he slept with. I keep telling him it's not right to be friends with someone he slept with and he tells me I can't decide who he can and can't be friends with. I had also said that I don't want her at our wedding because it makes me uncomfortable and he said then there's no wedding because I can't stop who comes. He will invite her no matter how I feel. Any thoughts? He thinks I'm being irrational and I get angry over nothing but I think this is extremely valid.