How can I get my ex to take an std test? HELP PLEASE!!! :(?

My ex bf as of 4 days ago cheated on me and slept with another girl. I want him to take an std test to make sure that he is clean. I dont think that he will want to. How do I make him? should i threten him if he says no, should I tell him that if he doesnt I will spread a rumor that we both went and got tested and I was clean, but he has an std, or should I tell his mom about this and embar him. Should I tell her that I am concerned bec cody has slept with so many girls that he may be in danger of having an std? We dated for a year and 7 months, im heart broken and want him to feel pain. I also want to know if I may have anything.