HI pullingtaffy,
I somehow ended up on this forum and your post and decided to sign up and fire you a crack in hopes of lending you a helping hand.
I am somewhat startled at the amount of people telling you to head for divorce; it's an option, but definitely not the first in line.
The first point I noticed is that you are having significant issues with your DH. It appears you have had no sex in 5 years, and I am assuming there are probably a slurry of other issues involved here too which you may not have mentioned.
The first thing that stands out to me is your complete lack of communication. It sounds like neither of you knows how to communicate and are simply making do with what you have. Naturally, you will get frustrated, and many emotions will accrue over the years. You probably feel unloved, rejected, lost, confused and so on.
It is also no surprise that when a particular direction isn't working that you will naturally gravitate in another direction in hope that you may find some light. In many instances, things that you may have "buried" in the past might re-emerge in your conscious and appear to be that bit more tantalising - not because they necessarily are, but the rejection and lack of love is leading you down that path.
This invariably leads you to explore and now you have found someone who understands you. Maybe you feel that only another woman can understand your lack of communication, rejection and confusion since women understand each other better emotionally than men do. so it may simply be a case of "she gets me" rather than "I am gay".
But you see, this is all too deceptive though, isn't it ? The problem here is your lack of communication with your DH and rather than addressing that you are running away. This might feel like the solution but these behavioural patterns have a tendency to repeat themselves.
What that means is if things start turning a bit pear shaped with your new partner, then you will do exactly what you are doing now. Close off, lose communication and look elsewhere.
The fact that you have explored all of these things behind your DH's back is a testimony to how bad the pair of you are at communicating, lack trust, and openness and such a simple thing is having dire consequences.
The other thing is your children. You could jump ship but regardless it will effect your children. Children are very sensitive to these issues and there are many statistical psychological studies that show how single parenthood can have significant effects on a child's mental, emotional and material development. They are more likely to have mental issues, self harm, under perform in school and so on - divorce is NO joke. And if things turn really sour and one parent ends up disappearing then they will also have to deal with rejection, confusion, and sadness which will negatively effect them their entire lives.
I think a first cause of action is not to hurry for the papers but to develop you ability to communicate with each other and try to rebuild your relationship. Maybe a good start is to write all your emotions down on a paper so that at least you have some concrete representation of what you are feeling at this instance. You could either write to DH, or you can list the things you'd like to discuss with him and set a few hours aside to talk things through and discuss how you two want to move forward. You need to be frank, for your sake, but for your children's sake too. If lack of sex is an issue, you need to discuss it - why doesn't he want sex ? what could be going wrong ? maybe he's addicted to adult sites, maybe he's stressed out at work, maybe you aren't doing things that would make him feel more eager to want sex. There are so many possible causes and YES it may hurt to hear some of those things, but you need to if you want to move forward.
If that doesn't work, then you can always try couple counseling.
With regards to sex, one possible cause could be the food he is eating. If he eats junk, and has little fibre in his diet that could be killing his libido. There are many foods that can even increase libido, not just viagra. You see, these are things you need to think about and consider.
Life is hard, relationships are tough but working through problems that arise develops you as an individual, but also as a couple - running away is never a solution. Throwing in the towel after you have explored all options is something different however, but judging by your post, It looks like you may have some possible things to try before calling it quits.