Monogamy: boundaries or manuals?

I’ve been married for about a decade and we started out monogamous, but my spouse, for reasons I not only understand but also completely support, asked to open the marriage from not long after the honeymoon. After we discussed and weighed the cost/benefit for a few years, we were no longer monogamous, and though I had reservations, a few months ago I came to really appreciate our arrangement because I started sleeping with a close friend and came to genuinely love that person on a significant level that enriches my life deeply (while still loving my spouse completely), but that emotional intimacy frightened my spouse. Now my spouse wants monogamy and regrets opening in the first place. I have complied.

Although I believe I’m not responsible for my spouse’s feelings of jealousy and insecurity and therefore I think asking me to be monogamous now is a “manual,” I don’t think it would be best for the marriage to just continue on and to stop being intimate in any way with my friend now that consent has been withdrawn, and my spouse has stated that divorce would be the consequence should I continue to be intimate with my friend, and sometimes it is threatened even if we merely remain friends at all, which I think is excessive because this friend is integrated in with my social network. We also have young children and I think that would be a foolish choice for my spouse to react in a way that could cause them unnecessary insecurity, but I want to operate on a level where I am not simply reacting to attempts to control my behavior.

My spouse is jealous at any contact or friendship at all with this person, putting down my friend, and constantly trying to access any conversations on my phone or computer. To be fair, my spouse and I used to have open phone and computer policies because we had such good communication and trust, but now my spouse is looking for reasons to fight: any kindness or affection from my friend, even the most benign jokes like my friend and I had from before, and looking at other private conversations with completely platonic friends looking for faults and evidence of betrayal. In response, I have changed all my passwords and leave everything locked because I do not feel comfortable being policed and have explained the reasons and my spouse agreed that looking for evidence of problems was causing unnecessary drama. I also don’t engage in discussions where spouse insults friend. I remain warm, deeply appreciative, and loving toward my spouse, looking for ways to strengthen us without getting distracted by the friend.

We just now had a tense conversation where my spouse assumed I was writing my friend here on my computer, and when I said I was seeking advice, my spouse wanted to know what bothered me that I’d be writing for advice late at night. I replied honestly and then it became a whole irritating discussion again which turned into a whole “that person or me” discussion I did not particularly want to have, because although I would prefer to stay married, I do not want to feel controlled.

I love my spouse and am content with my marriage on most levels. I know I am responsible for my feelings and will ultimately be as happy with or without my marriage. I simply dislike the attempts to control me. I’m trying to let my mind generate ideas about how to have the life I want, which includes being as intimate as I want with both my spouse and my friend and dealing with everyone as an emotional adult where no one is under the illusion they can control me with their insecurities and being clear about my boundaries, my spouse knows this is my goal and finds it infuriating. My actions are to remain monogamous and patient and positive with my spouse while everyone else catches up and learns to manage their emotions better.

Where are my mental errors and what can I do to better deal with this situation?