UGH, I can so relate!
I have a friend who insists that if I tell men I am open to polyamory, I am just setting myself up to being used, and that they will leave me after getting what they want, and so on and so on. She met a lover of mine once and the next day referred to him as "your man" in an email, even after I explained to her that he is a friend I am physical with, not a boyfriend. I replied and told her he is not "mine" and that we enjoy our relationship without those kinds of designations. She always says, whenever I talk about poly, that she and "all her single girlfriends" are jealous whenever I tell her I have even one guy, never mind that I want two or three or four. She used to say this even when I was with Shorty, whom I only saw about once or twice a month. I think she even once asked me, "Don't you think it's selfish to want more when most of us can't even find one?" Her mindset is so wrapped up in monogamous stereotypes of the poor single chick looking for Mr. Right everywhere she goes, that she can't really hear what I'm telling her about my choices. And sometimes she has me feeling like I must be nuts.
So, some people will never understand. Just don't let there refusal to see or hear what you're saying shake you and how you want to lead your own life. Some people aren't the right people to tell.