RP, I think there are a few things you need to do.
First, you just really need to ask yourself what you want. Not what you think will be best for everyone, not what you think might be expected of you, but what YOU want. When you're with your new friend (NF for short?), do you feel like you want to get closer, share more emotional and physical intimacy? Is there an urge or a tug that you cannot shake that you feel you must explore? Or are you perfectly satisfied with a close platonic friendship with him? It sounds like you want more than a platonic friendship, since you told him you'd like to go out on a date with him eventually.
Once you figure that out, you will know whether to back off and ask NF to respect your boundaries or to start talking more seriously with your current partners about this. And then take baby steps to renegotiate your agreements and boundaries with them. Maybe NF will be more like a FWB than a partner. I know that's not usually your thing, but it could work.
Regarding PN and Mono (I'm not including Derby since she's already read this and written to you, so she's in the loop), there is also nothing wrong with saying to them how confused and scared you are. "Hey guys, I'm confused and don't know what to do, and I worry about how you would feel if I have an additional lover, and I want to do everything I can to stay connected with you both." You say that you're afraid Mono will hit the roof - just try not to get defensive and wind up in a fight if he does. But somehow I think he won't. I think he will probably be willing to talk as much as you need to with him. Ask him to examine within himself if he can handle it or if he thinks he would lose interest in you. Ask him how committed he would be to you if there was one more man in your life. I know you will not take any steps unless you have reached some sort of agreement for how it can go.
NF is not Leo, so put that whole drama out of your mind. And realize that you and all your loves are not the same people you were when you were struggling with issues around that relationship. Everyone grows and changes.
Last edited by nycindie; 04-24-2012 at 04:03 AM.