My Best Friend Wants to F*** my Boyfriend

My best friend wants to f*** my boyfriend... again. When me and my boyfriend started going out I was away at school and we are in an open relationship. He was h****​ and I wasn't​ around to f*** him so my best friend volunteered. Now I love my best friend more than most people and was completely okay with them having s**. That was a while ago and honestly my best friend is kind of a s***. She has s** with people she don't know all the time but this is a recent development. Now my boyfriend lives with me while I finish up school so we don't go home nearly as much because we both work. My best friend said next time we come home she wants to have s** with my boyfriend one on one but I won't let her because she won't get tested. Now she's mad at me and calling me a hypocrite.
Confession: She stupid as f*** if she think she going anywhere near my boyfriend's d*** with there being a possibility she not clean.