thank you for that additional info. At this point, there's no sense in pointing fingers or deciding who to blame. With that said, there's nothing wrong with wanting a full and passionate sex life. Keeping in mind that sex does get boring and ordinary after being in a relationship for a long time, and it takes both people to be willing to put more into it to make it exciting and passionate, but it's not something that can be done by one person, both people have to be willing to put everything into it and make it attractive and exciting for both. This takes commitment. When someone says they do not enjoy sex anymore, the question would be, why don't they enjoy it anymore? If your heart was not in the relationship, it's possible that you caused damage to the relationship that could have caused this reaction. At this point, if you are saying it's too late, then there's nothing to do but to put your cards on the table and let her know that ...unfortunately, there's just no easy way to do it.
I understand how you feel about not wanting to hurt the kids, and believe it or not, it is possible to do this without causing too much damage. Of course they will be hurt, and most of all they will be hurt, and feel guilty. Children always think that the reason this is happening is because of something they did, that they are in some way causing you to leave. So it will be important that you and your wife are on the same page about what to tell the children. Neither of you should bad mouth the other, and should respect each other at the very least when with and around the children. Let the children know this is not their fault at all and that you will always be there dad, and be there for them. It's important not to introduce other partners to your children for a good amount of time, and to always keep your word to them, as you will be under their scrutiny for a long time to prove you haven't changed and will still treat them the same way. I welcome your thoughts, let me know if you want to talk more., I'm here anytime.