jenny - sorry this is so long but I hope it might help.
I have come to a sort of clarity and understanding of myself due to DH's affair. There was a lot of resentment between us for various reasons in our shared past. We have been together for 26 years (married for 20 this October). In that time a lot of water has passed under the bridge - some of it very troubled indeed. It left it's mark but neither of us had the courage and honesty to address this.
Many years ago I had what amounted to an emotional affair with someone at work - he was everything that DH wasn't. But he blew it when after nothing but a bit of hand-holding, some very intense conversation and a lot of staring into each other's eyes
, he told me he loved me more than anyone he had ever met, was going to leave his gf and wanted me to leave DH. I ran like a scalded cat and never went near him again - I left that job as soon as I could get another one. DH never found out (until recently) but my memory of it hung between us like a bad smell. It took me a while to get over the OM and I used to retreat into my memories of him when things with DH got stale and boring. How could DH compete with my wonderful fantasy man?
Our marriage has been stable and strong in a practical sense but not passionate or loving in the way that most people would think of it. It was a sort of living death emotionally.
I suffer from depression. Have done on and off since my teens, worse since my second child was born. It has made me less able to conduct a healthy relationship. I have sought medical help but it has been of limited use. DH has been sympathetic but it's taken it's toll. We reached a nadir over the alst few years when we hardly communicated at all. It wasn't my fault but neither was it his. Life happened to us and we didn't know how to handle it.
DH began to develop an overly close emotional connection to a woman at work - she was looking for support in her horrible marriage. She was attracted to him as an older man who seemed the opposite of what she had known. He was vulnerable to this as a man in MLC with a cold ailing marriage. This does not make it OK. THey were both guilty of huge selfishness and the fallout has been immense. DH can't forgive himself, I have had to deal with so much pain and i daresay the OW is in a mess too.
BUT.... and this is important, the affair has acted like a sort of kick up the arse to both of us. We are good people who love each other a great deal. We have had to be painfully honest and there have been many tears shed. I have learned that I don't want to be with anyone else, and so has he. I have also learned that happiness isn't hard - it can come from anywhere, but it can't come from another person. Looking to DH (or to anyone else) to make me happy is absurd.
Tell your DH what has been going on. Let him react in his way. He may surprise you by how much he loves you and doesn't want to lose you. You might find that in fact you love him much more than you thought and don't want to lose him either. Honesty!! Be honest and open. That is the only course that makes sense. If it all falls apart, then leave. Be happy that you have tried to make it work and had the decency to give him honesty.