Presumably when you first met your wife, and you felt that she was "the one", there was romance and sex and communication. That can break down over time, ESPECIALLY after having children.
My H asked me to go to marriage counselling a couple of times and I refused. But he ONLY asked once he was already involved with OW and once he had denied my accusation that he was having an affair, AND he told me I needed marriage counselling because I had problems. Turned out I did. They were him. He was lying, he was spending our income on another woman, he was treating me like a skivvy and wining and dining her. We had 2 children too. He has left them with me, almost entirely, so that he can enjoy sexiversaries too. He was lying to me, he was twisting arguments to justify his betrayal to himself (and probably to her - it is always great to turn to your affair partner and say "we had ANOTHER blow out argument last night, she won't go to counselling and she doesn't understand me like you do, now get your kit off and SHOW me how you love me".
I am sorry, but there is no honest justification for having relations, emotional or physical, with another person when you have made promises to a committed relationship. You ALWAYS have the option of leaving the relationship. Having a break, shocking your wife into working on it for the sake of the children, giving her some choices. Unless you are a coward with no-self esteem, who can only make choices about your own life with someone providing some ego-stroking and validation so that you don't feel so bad - poor you. The truth is an affair is the most destructive way to leave a long-term relationship and marriage. It damages the children ( you have effectively told them that their mother (half of their DNA, remember) is not only not "good enough", but she is also deserves a high level of anguish and pain. You have given your children the message that half of their identity was worthless to you, their father. And these messages go deep into the psyche of children, just in case you think they don't.
I get sick of people saying divorce happens all the time. Yes. And death happens even more frequently. That does not mean that we expect people to get used to it and for it to hurt less when it happens in THEIR own family.
I feel sorry for you, honestly. I would be very interested to know if you think you had any imperfections (real ones, not ones designed to sound like good traits in disguise) in your marriage?
Anyway, sooner or later the sex will slow down with Anna. It may not be for another year, or five, but it will. She will become more demanding, she will start to find things you do annoying. Your relationship will hit a point of age, where it does not involve constant gratification. You will start to wonder if she is not a bit annoying in some ways. But never mind, there are always more willing women who will take on the opportunity to win you away from her... unless she gets bored first and leaves...
In the meantime, what of history, what of friendship, what of loving the same wonderful children in a way an affair partner never can, what of finishing each other's sentences, what of acceptance of one's self and others, what of acts of service that are NOT about getting anything in return (sex, gifts...)
We all loved the new part of the relationship, the constant sex, the constant compliments, the excitement of discovering another person's interesting life. But all things end, including the initial highs of a relationship. The middles are hard (children, jobs, lack of free time) for EVERYONE in a relationship. But if you can weather those things, what about what may be found on the other side? I guess, you may never know...
I would be very interested to hear if you and Anna are still as happily sexing away in 10 years. Good luck with that...