I'm going to take a bit of a different tack here. As I was reading the husband's original posts, I was struck by how charming the whole situation seems. (He and his wife both fell in love with the same person? How cute!) And I felt that overall, his relationship with his wife seems pretty good, all things considered.
I know some people want to come down strongly on cheating. But this seems like a prime example of a case where cheating should not be that big of a deal or that big of a betrayal.
Yes, Messymess cheated on her husband and initially was lying outright about it. But, meanwhile, Polyscared was himself engaging in emotional cheating (albeit one-sided cheated since the object of his affections was in the dark about it). For months, he spent hours a day thinking obsessively about his crush on his wife's best friend, tormented with fantasies about her, confiding these feelings to his own best friend but not to his wife. His connection with his wife drifted during this time, in part because he was being dishonest with her by not sharing the fact that he had fallen in love with someone else.
Please appreciate the adorable, charming aspect of this story. A husband and wife each fall in love with other people, and keep that love secret from each other. Then it turns out they have fallen in love with the same person. How cute is that! Think of it as a twist on the "Do You Like Pina Coladas" song.
Messymess clearly feels bad about the cheating. Certainly, it was wrong to act on her feelings before talking to her husband. But I can imagine a situation in which a close, cuddly friendship progressed slowly into fooling around, until suddenly it was too late and Messymess found herself in over her head. (Yes, that's point where she should have confessed all to her husband instead of hiding her text messages, but people don't always do the right thing, and Messymess knows she did wrong).
I think there is also some leeway for forgiveness in a situation where both members of a married couple have been together since adolescence. If you have never had feelings for anyone else since you were fifteen, you will have no idea how to process those feelings when they happen. (It's pretty rare, in fact, for anyone to have feelings for only one person throughout their entire lifetime. But no, you don't always have to act on it).
For what it's worth, it sounds like your love for each other and your communication with each other are solid. I think you'll get through this.
Now, as for the main problem. Polyscared feels left out of his wife's relationship with her best friend. Well, unfortunately, it sounds as if the best friend simply isn't in love with the husband, and is maybe only halfway interested in having sex with him.
That's sad, but that's just sometimes the way it works out. In most threesomes, two people often have a stronger connection to each other. It's very rare for the "third" to connect equally with both members of a couple. (Maybe in this case, the best friend simply doesn't experience romantic feelings for men).
Polyscared, you don't really have a right to demand that your wife only be involved with her best friend if you can be involved with her too. You do have a right to ask that your wife stop seeing her friend and work on your marriage; but you also may choose to allow your wife to have a poly relationship that does not include you.
It does sound like the best friend is a bit immature. If she really can't handle any type of emotional communication, she might not be the best candidate for either you or your wife to be involved with.
On the other hand, she might simply have a different communication style than you are familiar with. Some people just require more patience.
As for the sexual problems: stop having threesomes with the best friend if you can't talk to her about basic things, such as how you like to be touched during sex, and how you have feelings for her but feel unsatisfied in your interactions with her.
(Definitely take alcohol and pot out of the equation entirely).
Also, read as much as you can on this forum to see how different forms of poly work for the various people who have poly relationships.
Single, straight, female, solo, non-monogamous.