S., I have not read the other responses - yet. I will.
I just want to say that I am sad for you. Sad that you have a husband who mocks your most intimate space. Take away all the fun and games, the commonalities, the intellectually stimulating conversations, and it appears you have a husband who does not love you and respect you enough in the bedroom to make an effort.
My marriage is almost the exact opposite of yours. I have almost no sex life, but we always cuddle, hold hands, kiss, dance close, he rubs my feet, and scrubs my back in the tub. And he tenderly caresses my large breasts. We're just old and tired and don't have much energy for 'going all the way."
Even before my marriage, the man that I was intimately involved with, where we had sex every single day, there was always cuddling before or afterwards. It's actually the cuddling that led to the sex. We just loved spooning, anywhere we could. Watching TV. Reading. Talking. etc.
As a matter of fact, I've never dated a man who did not cuddle. That is too important of an aspect for me in a relationship. I'd be an emotional wreck without the physical intimacy.
I just think there's too much to conversation and analysis in your sex life. If this were me, I'd stop offering any sexy threesome talk, and I would completely shut down the next time he brought it up, even if you were in the middle of the act. I'd get up and walk to the shower. But you have to know what it is you want and what it is you don't want. You sound so focused on pleasing your man, that you are ignoring your basic, primal needs of wanting intimacy with him. Please don't think that adding a 3rd party will ever increase intimacy with him.
I also suggest that your intellectual connection is a cover up for the lack of physical intimacy.