I had thought we had found a way to handle the situation that suited us both, but 8 months ago, he suddenly confronted me with the fact that he had met another woman in the internet. A submissive woman how wanted him to become his online dom. (I didn't know that he was able to switch, but that's another story).
After many tears I agreed to their relationship. He told me that I came first and that he would end that other relationship if I insisted.
Well, after a couple of months I did insist, but he did/could not end it. – And that was a real shock for me. It was proof to me that she was so very important to him. More important than I was.
Regardless of what you want to call it, there is a need in his life that you were not able to satisfy. That isn't your fault. It's not his fault. It just is. It's a myth that society perpetuates that your marriage partner is supposed to make you completely happy. It's an ideal that few relationships ever achieve. So first thing is get rid of the guilt and humiliation. It's nobody's fault.
My story is that my libido is about 20 times higher than my wife's. I also went the online route, but we talked it out before I get too involved. In the last 2 years, I've been involved in a friendship that has grown into a romance. It has changed nothing I feel about my wife.
My recommendation is find out is are you lacking anything (besides trust, you're going to have to repair that.. if you want to) in the relationship. Is he still giving you all the attention you need? Is he shirking household duties to be with his new lady? If nothing is actually missing, then what is that you really want? I know you say you want him to be all yours, but you don't own him even if he wasn't seeing anyone.
I would recommend Opening Up.
Theres a lot of information on both inital relationship damage as well as dealing with different sexual needs.
It may help, it may not, but it's a short read.