Crazy one night stand...

My fiance slept with this girl while we were broken up.. well when he dropped her completely to get back together with me, she claimed she was pregnant. He used a condom and he only slept with her once... and now she's telling his mother she was raped just to try to get his attention...who does this? Why? She's freaking married to a military man who's deployed right now for Christ sakes... Why my man?