I just found out my boyfriend of 5mos has a fiance in another state. What do I say to him?

Well I been with my boyfriend for 5mos now and i just found out he has a fiance. The woman who is his fiance he claimed is his friend of many, many yrs ago but he continued to lie about her. She lives in another state. He says im the only one for him I know its a lie. How i found out I called him through this thing called Spoof pro which u can change ur number and voice. SO basically he told on himself now he wont answer his phone. I think he knows i know but im not sure. What do I say to him or how to I begin to tell him I know ur engaged to another.