Is there anything that I *can* do?
It kills me to see a friend hurting.
You could tell her you see that she hurts. And could ask her if there is anything that you could do for her that is appropriate for the situation to help alleviate some of her burden. Walk the dog? Make a casserole? Take her to a movie and air her out?
Be leery of any "put me in the middle stuff" but other than that -- choosing to be compassionate toward a suffering soul is not a bad thing.
(Knowing) that DH is a source of the pain kills me even more. Are there any probing questions that I can ask DH in hopes to help him figure his head out?
His head sounds fine. He is clear about where his emotions are at. He's just on another square than her in love theory.
It is what it is there in the heart space. You cannot control his feelings.
But in the BEHAVIOR space? You could point out that while you understand he feels different, is he aware that his continuing his behavior (being her casual sex lover when she wants more than that) is causing her suffering? And you suffering?
Is he planning on stopping his behavior so he does not continue to add to her burden? And doesn't add ugh to you watching your DH behave kinda sex usery toward your friend? Because if he KNOWS she is into him like that and he is NOT into her, this is not longer two people agreeing to come together for a casual sex share.
She is responsible for herself -- she could say NO. She could stop sex too. But if she's in lala land with her crush she may choose less than healthy things for herself.
He is responsible for himself. He could say NO to cut it off and be a gentleman. Kind but firm. "No, I like you, I see you want more here. But I cannot share casual sex with you when it really isn't casual any more for you. It would be using you like a thing and not treating you like a valued person. Toying with your affections -- That is not right. You are a good friend to me, I want to be a good friend BACK."
You cannot control his behavior. But you CAN give him feedback on how YOU are feeling with it all and check that he is indeed, AWARE.
If this is friendship and casual sex for him, why not dial it down to just friendship and drop the casual sex? You could ask him that.
OSO has said that he just can't let himself explore his feelings for me unless he has all the pieces of the puzzle. I feel that's not very fair to me, but I do see why he could feel this way.
I don't know what that MEANS "pieces of the puzzle" but... that is his personal limitations. Until he decides otherwise, it is what it is. *shrug*
OSO is afraid that if he does explore feelings for me and falls, DH will decide to pull out altogether, and even though both of them (DH and Fiance) have told OSO and I that if they separate, then it won't affect us, we're not blind... we know that it will. And that scares the shit out of me more than anything else, because I've fallen.... hard.
That's TWO things.
1) OSO fears
You could talk to him about his fears and whether or not he is willing to work on them at this time.
2) DH and Fiance believability.
You could choose to believe them. Or not. It is up to you.
You and OSO (assuming he is willing, and he doesn't sound like it right now because of fears)... You and OSO could ask them in quad about that -- "We would like to deepen on the (OSO + me) layer.
Both of you (DH and Fiancee) have told us before that even if you separate, it would not affect us in the sense that we could not be romantically involved (me and OSO.) Does this still hold water? Are you prepared for this? Is this the best time?
Because we'd like to move forward on our tier while still supporting each of you in appropriate ways and things develop on the (DH + Fiancee) thing wherever it is that it may lead. Even through a break up and settle into a friendship. We'd be willing to hold off 3 mos, but you both need to be aware that feelings are growing here."
Maybe something like that.
Talk. Sort yourselves out. People are not mind readers.
Don't offer to do things you don't really want to do (like hold off 3 mos) but if holding off so the TIMING of when you and OSO deepen more is in a calmer zone, perhaps that is worthwhile to consider.
A place and time for everything, and everything in the right time and place. So... you could talk to your polyship people to get an assessment on the things, the times, the places on the table here.
Get the lay of the land... What's going on in all the polymath tiers and how can this polyship navigate through some potential turbulence safely while allowing space for things to change, grow, and flex. Life is nothing but "journey."