My boyfiends little cousin is spreading lies about me to cover herself what do i do?

......Since your boyfriend believes you and knows you're being maligned by his cousin, "he" needs to step up and straighten all this up for you. Don't use false threats as you might be found out and then there goes your credibility (don't ever lose it). No one will believe you after that happens! Do not seek to take revenge, you only have to wait (patience is a virtue & good things come to those who wait) the cousin sounds like she will be found out soon enough!!!!Good Luck....tell your boyfriend to help with the mess "his" cousin made!!!!!!!!!