Do I trust him?

I was previously married and faithful into marriage. I had a man I fell in love with the moment I met him he will be called Xavier, but again I, married. Xavier would text me out of the blue calling me pet names and being cute. I told him to stop and told his best friend to have him leave me alone. 3-4 years went by, I am now divorced. I contact Xavier and we start dating. I being stupid didn't use protection and he gave me an std. I confronted him and he gave me a line like some guy warned me about a girl I dated. Xavier said "I didn't believe him". Xavier also said he has never had an episode with the std. I asked why he didn't just  go get tested to be sure. No real response was given. Should I believe that he REALLY didn't know he had this?