First and foremost for me-I'd rather you write a book then ask for advice without giving me enough info to work with.
So don't feel guilty about having to detail it out.
If I understand you correctly-you love two people. At some point you have dated each of them and they have dated each other as well. Now they want a triad with you. It's fun-but you are struggling with how their sex life seems to be bouncing along to greater heighths together then with you. You don't say WHY but you do say that you've never had an orgasm and it would seem based on what you are saying that neither of them have any issue with that.
THAT detail right there puts me on pause. My reason is that if you have NEVER had a relationship then NEITHER OF THEM was able to get you there when you were dating them AND you haven't found anyone else who has or been able to do it yourself. If you can't get off-that is going to seriously impact how much you CAN enjoy the sex and intimacy with them which is going to guarantee that they become closer in that arena then you by default.
So my FIRST thought is that you need to resolve that.
I could give you a number of suggestions on that topic if you like-either on here or in a private message. But am not putting them in this post as some people would be offended at having someone just pop out and say "have you tried xyz etc" without making sure they were comfortable with it-so let me know if you would like suggestions.
talk to your gynocologist. SERIOUSLY.
get a mirror and study your body. SERIOUSLY.
I had already had my first child before I figured out how t orgasm. It was a horrible point of contention with my then boyfriend and it was terrible for my self-esteem which in turn made me more possessive, paranoid etc. Resolving that issue brought me around SO FAST to being open minded, un possessive, confident etc.
Once you solve YOUR issues with sex, then you can work on being a part of enjoying the rest.
Also-if these two TRULY love you-then they need to help you in figuring it out.
I read this that you are a woman-please correct me if I'm wrong!
But that assumption in place, are you internally aroused?
Do you know?
Are you shy about your body parts?
do you feel like you can relax completely when you are naked? partially clothed? dressed? At all?
Have you been abused or in abusive situations/relationships?
all of those can effect your ability to have an orgasm.
Don't give up-there is a solution. Just have to figure it out!