I agree with gatorvol64 totally.
OK, my current thinking is that as long as Mr 2TT feels as threatened as he does, no compromise is possible because Mr 2TT's fears are overwhealming his perspective. Also, Mr 2TT please, please, please re-read your last post. I hope you can see the pattern of how you constantly 1) refuse to "own" your own feelings -and 2) you subtily push the responsibility for the consequences of your not "owning" your own feelings onto others. The paragraph that you wrote that gatorvol64 quoted above is a perfect example of that. I do not mean to sound harsh, but this is what I am seeing. I am hoping you can also see this too now that it has been pointed out?
Another example is when you say you are not angry! You are angry! Own it! That you are probably more angry at yourself for getting your relationship into this fix than anything else is one thing, but then projecting that anger and the fears and doubts that creates onto others is really making things a lot more confusing for you! If Mrs 2TT says she can forego the poly relationship with Mr P, thrust her that she can! You "own" your feelings...let Mrs 2TT "own" her own feelings! Will she experience a sense of loss? Maybe, but let her "own" that for herself! Don't try to take that away from her and keep things stuck! Letting her do that will let you "own" your own sense of loss that playtime is over... for now!
As for what to do to survive all this: Read what VegasLee already posted until you really understand what he is saying.
Mr 2TT, you have to stop both swinging and any poly adventures because right now your fears are clouding your perceptions. Your desires to play overcame your own intentions to restrict things to swinging and your own self imposed rules, so you can't swing. Your lack of understanding of what poly actually is and your talent for putting yourself and others into false double binds means that right now you can't do poly either. You want to pull the stop lever, yet you say you cannot! False double bind! You are sending Mrs 2TT mixed messages.
Mrs 2TT, I am hoping you can see what is happening here, and I am hoping that you can put your intentions to preserve your relationship ahead of your desire to fulfill your long standing feelings with Mr P, you have said you can do that and I believe you. I hope you can also see that although it might not be fair, you may have to be the one to pull the stop lever and keep it pulled if Mr 2TT waffles and can't get congruent with what he really wants to have happen, and until Mr 2TT is capable of congruently expressing and acting on his feelings in real time. Mr 2TT is feeling far to threatened to be making good choices or seeing things clearly, and hey that is OK, it happens. Once Mr 2TT's fears subside, maybe you two can have a more constructive discussion about things, but right now I do not see how you can, Mr 2TT's fears are too severe for that to happen right now.
No one is "right" and no one is "wrong", it is what it is. What needs to happen is for you two is to take your relationship back to a point where the sex and love is about and between you two alone. For now anyway.