Having read through the further comments I am going to make a post so that I can try to clarify things although I am sure I won't be able to fully do that to everyone's satisfaction!
Firstly, there are SAHMs in this world who do not need to work and I don't feel that I have to explain my situation any further. Aside to say that I have never claimed a penny from the state and so the fact that I don't have a job is really nobody's business.
Secondly, DH and I had a frank an open discussion last night and have come to an agreement, for the time being. We are not planning to divorce because neither of us want to cause the huge upset to our family that it inevitably will. We will attempt to resume a sexual relationship (and that will take effort and compromise from both of us and not just from me). However, both of us are free to do as we wish outside of our marriage. We both have lives of our own, friends of our own, interests of our own etc and we feel this is the best solution for us currently.
Our children are still our children and just because they are at university or studying A levels doesn't mean that they are not dependent on us and still very much a part of our family. We both have their well being in all aspects at the very top of our priorities.
And for the posters who were so quick to judge me for my emotional affair, yes it was wrong of me but it was't done as some kind of revenge for my husband's affair. I still don't feel that it was relevant to the question I asked in my opening post - I didn't reveal that DH had an affair either - even if it was 20 years ago. It actually doesn't matter how long ago it was but it happened. But neither is relevant to the question I asked - there seems to be an entitlement of knowledge/revelation by some posters. And to put people's minds at rest (as I am sure there will be assumptions made), the OM with whom I had this emotional attachment to is single and has no children - and is still in contact with me.
I do love DH and he loves me - ours might not be a conventional marriage but we care deeply for each other. I hope that explains a little of why we have decided on this path.