he's using prostitutes ...

Hi, I've posted this anonymously because I feel ashamed.
I've been with my partner for 4 and a half years, in that time I've always been loyal and faithful to him.
He gives me a fantastic life, I have everything I want both material and emotional.
I'm pregnant with our second child.
We have a fantastic sex life in fact we have sex at least once a day!
But he's using prostitues behind my back.
I've found the numbers on his phone and I don't know what to do. Is it me? Is he an addict if I'm not enough for him? Please don't judge me.