I’ve felt like this twice in the past; however, I certainly never acted on it the way you have. When it occured for me both times, it didn’t go beyond text message flirting and the like because just the thought left too much guilt. Shortly after I found myself doing this, the relationships I was in at the time dissolved, and it was not as a result of my behaviour.
The reason I’m letting you know that is because, in hindsight, I realize that the relationships I was in were not satisfying my emotional needs. Yes, there was lust and desire for the physical, but it was fuelled by my need for my emotional intimacy. In on situation, my boyfriend at the time was not affectionate or loving. He was controlling and didn’t ever do anything to make me feel good. Every nice comment and action that came from him was a result of ulterior motives to get something or generally manipulate me. He didn’t make me feel loved, beautiful, happy, or wanted. Normally, I wouldn’t say it is his fault alone (I didn’t speak up, after all), but because I realized all he wanted was to manipulate me, in the end I do blame him entirely for pushing me away and making me need something more. Text message flirting with a then-coworker satisfied me in ways my relationship did not.
The second instance I was in a relationship that started out wonderfully. Over a couple months, however, I noticed that my boyfriend had become distant. He didn’t cuddle me in bed the way he used to, he didn’t try to initiate sex, he wasn’t as interested in me coming over as he used to be, he never tried to hold conversations with me anymore. When I tried to talk to him about it — and I did numerous times — he was stone faced and would only have a conversation if I let him play video games during (yes, turns out he was an asshole). I’d say something requiring a response and he’d not answer. When I insisted for one, he’d tell me he has nothing to say and that I’m being crazy and emotional. This led me, once again, to find comfort and intimacy — this time with someone I had been seeing for a while before my boyfriend and I had gotten together — in the form of flirtatious text messages. Well, a week later he felt even more distant. While I was over, he had a shower… During which my gut told me I needed to get to the bottom of things, so I went into his messages on his phone and Facebook. I found out he had distanced himself, whether he realized it or not, because he’d been sleeping with a coworker for at least a month. It could have been longer, but it was difficult to tell.
In any case, while my behaviour was horrible, I can see now that my desire was a result of the saddness and dissatisfaction I felt with my partners. With my current SO, I am incredibly happy. Rather than being in a one sided relationship where all I do is give love, and am not loved equally in return, he returns my love just as strongly. He is affectionate, considerate, loves to spend time with me, is concerned for my well being, makes me feel beautiful, and is genuinely loving. By caring for me in such a way, I am fully emotionally and physically satisfied, and the idea of repeating the behaviours of those two relationships in my present relationship… Well, the thought just appauls me.
I would suggest that what you think is an addiction to flirting and sex, is actually a psychological response to you not being emotionally satisfied. My personal opinion is that, in a romantic relationship (not ones based strictly on a physical exchange of sex for physical satisfaction alone), if a person becomes emotionally unsatisfied, the sex dies. Only when you and your husband get on the same page emotionally by sorting out your issues and opening up lines of communication — I suggest counselling — will the physical intimacy return, and hopefully your desire for gratification outside your marriage will also disappear (I suspect it will). Either way, you need to confess to your husband what happened. I think that is crucial if you two want to move forward. He may decide he doesn’t want to continue being with you, but that is the price of your actions. If the relationship is strong enough, it will survive. If it is not, it won’t. Easy as that. And if he is unwilling to try to go to counselling and make changes even before he knows of your infidelity, well, sorry to say but then neither he nor you will ever be happy so you might as well cut your losses.
Edit: I just saw that you replied saying counselling is not an option and he will not go… While I’m typically against ultimatums, I think you need to set one. Tell him if he wants to try to save the marriage and be with you, he will go to counselling. If he does not, you will walk. I know it sounds harsh, but you cannot live the rest of your life in an unhappy marriage and cheating on your husband. You need find happiness, and this is not the way.