Problem with a lying partner

I’ve recently started this guy and everything has been great until recently. I found out that his roommate is a female. Which he lied to me originally about it. We’re suppose to speak about it more in person. I took it upon myself to do some investigating and found out it’s his ex fiancé. He doesn’t know that I know. I don’t know what to say or do. I have been to his place before and a person has been there when I was there but I figured it was his guy roommate he told me about. He said its nothing like that but I have trust issues and don’t know what to do. Help please