This is an interesting thread.
I understand what you are saying. Essentially, in your mind, you know how things stand. You know what your husband means and you know what your friend and his girlfriend mean to you. You know their places in your life.
You are concerned that if you tell your husband all of your true feelings, he might freak out, panic, see it as more threatening than it is and try to put an end to the situation. Do you rock the boat and risk losing one of these things that you enjoy.... or do you keep quiet, with everything you enjoy, unable to fully enjoy it out in the open?
So you're probably thinking that you don't want to cause him undue stress... if they are not a threat to your marriage and he keeps believing they're not a threat... why rock the boat?
I believe in a bit of an abstract concept, which is 'reality vs perception'.
I'll use myself as an example. I have a primary girlfriend. I have a casual, secondary girl that I'm sleeping with/friends with. The reality is, I love my girlfriend, I do not love my friend in the same way. My girlfriend's perception is the same as the reality. And she's mostly unthreatened.
Now, let's say I tell my girlfriend that I think about my friend sometimes when I wake up, that I smile when she texts, that we connect in a spiritual way. She might freak out and her perception could start to become removed from reality. She might think I'm fully in love with this girl. I'm not - so why would I want to cause undue stress? So I choose what I say to my girlfriend carefully.
In a situation like that, I am not completely honest
because I know that dilvuging every little thought in my head will lead to a silly situation that is not the reality
. I don't think there's anything wrong with a little discretion for the greater good.
However, if I was starting to want a deeper relationship with this girl, I'd have to tell my girlfriend. It wouldn't be right for my girlfriend to be happily moseying along whilst I am harboring deeper, secret feelings. My girlfriend has worked hard to overcome insecurity and be secure about my friendship with this girl. What a fool I would make of her if she found out that her suspicions were right all along. Furthermore, if I didn't tell her, I'd be taking away some of her rights in our relationship. For example - what if her line is: "I don't want you to have a second primary girlfriend". If that's her line, I can't just keep crossing it secretly. She has a right to put her expectations out there and see if they are still compatible with my wants.
In your situation, you want something. You'd be really happy if you could have that. How can you get it if you don't ask for it? You can't. Instead, you have a 'lite' version of what you want. Essentially, you've got all the components of what you want... but you can't fully enjoy it, because it's not out in the open.
Kind of like drinking champagne. Knocking back a $50 glass secretly in the kitchen of someone's party can be thrilling, but not completely satisfying. Slowly indulging in it, out in the open, because the host of the party has said they are happy for you to drink it, would feel so much better. If the host doesn't want you to drink the champagne... you can always leave the party and buy your own bottle to enjoy at your leisure.
By that, I mean, if your husband isn't happy with what you want... you do not have to stay in the relationship with your husband. Drastic, yes. But you do have to think about what you want and what works for you. As much as you need to be compassionate in relationships, this is still your life and you must chase those rainbows that fulfill you. The only thing anyone owes to a person they are in a relationship with is respect and consideration - they are not obligated to obey them.
Ah, posted this before I saw your update.
I've babbled enough, so I won't go on and on. But the best way, in my opinion, would be to sit him down, just spit it all out, tell him how important he is to you, make him aware of the reality of your feelings, for him, for your friend, give him all the reassurance he needs, be compassionate and kind to him.... then let him chew on it.... only he can decide whether or not he can deal with it...