My ex tells people that we had sex. WE NEVER HAD SEX, never even came close. HELP!?

I'm the sweetheart of my boyfriends' fraternity. We've been dating 2 years. My ex-boyfriend is in the same fraternity and we broke up mutually and amicably during our freshman year after only 3 months of dating. There was never any hostility between us and it seemed that we ignored that we ever dated at all. But now one of my best friend's tells me that my ex-boyfriend has bragged to people that he and I had sex during our short relationship and this is a complete LIE! I don't understand why he would tell people this, especially since he seemed so loyal to his Christian faith while we were dating and his purity values. Sex was never even an issue for us. I lost my virginity to my current boyfriend of 2 years, and he is the only one I have ever loved and have ever had sex with. I told my current boyfriend that my ex was lying to people about this but he feels awkward confronting him on the matter because my ex recently suffered a seizure and they're not really friends. What should I do?