Hi OP,
In my previous post I was focused on the fact that you feel betrayed by the fact that he was messaging other people and getting off in this secretive way that felt like a betrayal to you. I stand by the fact that you get to decide on your own boundaries and standards in a relationship.
The more I read about the dynamic of your sex life the more uncomfortable I feel and the more strongly I feel that he is not a safe or caring partner.
Many have addressed the coercive element of him insisting that you participate in a kink that doesn't turn you on, and he himself has admitted that he ignored your feelings or just pretended you liked it, he didn't consider stopping something that he knew was making you uncomfortable. This is such a big red flag.
You mentioned that you have not been very forthright in actively saying "I do not like or want this" and honestly, I felt this. Have you heard of the concept of "enthusiastic consent"? I have form for shutting down/withdrawing/going quiet/no eye contact when things take a turn that I don't enjoy or when someone is trying to initiate contact that I don't want. I feel like I should say "No, I don't want or like this, let's go back to x or let's take a break" but somehow the words don't actually come.
Recently I told someone out loud that I am not good at vocalising uncomfortable feelings, so unless I am actually saying "yes" out loud and looking at them, there needs to be some form of check in. And guess what? They listened and actually checked in! Even knowing that you were not enjoying the act that he wanted, it does not sound like your husband has ever really done any checking in with you.
I also second the interpretation that a PP gave; the special birthday request feels a lot like manipulation. I'd add that in my own opinion, an unhealthy number of people with authority issues and desire to dominate and/or humiliate are drawn to uniformed professions, and they privatte "indiscretions" are often protected by the image of being a uniformed public offical. If there is any element of this, it adds to the manipulation and he might actually be a very charming but nasty man who is using his position and his badge to emotionally isolate you.
This turned into an essay but I htink you have some serious thinking to do, and I think therapt on your own would be helpful. Many of us don't get off on PIV sex, but that's no reason to accept a sex life that doesn't satisfy you or to give up your boundaries to someone else's kink.