I know this must be painful for you. You sound very similar to me; you found the capacity to love more than one person after you entered a serious relationship. It sounds like you have had a very rough time of it....I'm sorry your loved ones are not more open to the idea.
If all else fails, I hope you will have faith that you could find another person to love someday that can accept you as you are. You could always find ways to meet people who are like minded and eventually one of them could blossom into a relationship. Still, I know you must dearly want the current people in your life to be more giving and open. You can keep trying to reason with them, but unfortunately the choice is ultimately up to them. I myself wish society was more open to the idea myself.
Me: K, female, 27. Married to Y for over 4 yrs (male, monogamous, 33). Opened relationship to E (male, monogamous, 27) in a relationship vee.