I'm really sorry if you're one of the MNers who've already read and replied to my ramblings about this on FB...
DH and I have been living separate lives since March. In early May, I started seeing someone new and fell head over heels for him. He said he was separated too, with two children on the scene. Our relationship was very intense; talking on FB from 7am until bed time, there was a real connection between us. I fell in love with him deeply. We talked about our future together. He told me I was "the one". At many points when we were together he would start crying, which he said was because his feelings for me were so strong and he couldn't believe how perfect it all was etc etc.
Cut to last week and I find out he isn't separated at all. I had it all out with him and he said he had no intention of leaving his wife/children but asked if we could carry on as we were as having me a bit was better than not at all. The utter cunt. I considered it BRIEFLY then told him to get lost. In absolute rage, I told him to tell his wife or else I would do it for him. He refused and begged me not to as it would destroy his children. I then saw his wife in Tesco. I was VERY close to telling her everything. I had his messages open on my phone ready to show her. I have literally thousands of messages and pictures that prove the gravity of our relationship. I was with my brother and he talked me out of it, telling me that if I was going to do it, I ought to do it in private and not in Tesco. Instead I settled for taking a picture of the back of his wife and sending it to him on Messenger saying "look who I am stood next to". He shit himself and threatened to go to the police, reporting me for harrassment/stalking.
I also found out that I'm not the only OW. He had a relationship with a woman from work, too. Ugh. The utter, utter cunt.
His wife was a teaching assistant at my DS's school. The utter brazenness of it all astounds me. I saw this woman every day in the playground and just thought of her as being the woman this new man was separated from.
This has wrecked me, truly. I can't really explain here how he made me feel and the depth/intensity of our relationship. I hate him and hope he dies but also love him still. I can't talk to friends about this; we have mutual friends and it will all just get out, all the ugly details. We'd agreed not to tell friends about us until we'd spoke to our respective ex-OHs. 
I hate how he has made me feel. I feel so stupid, hurt, angry, heartbroken, naive... I feel OK for a bit then the hurt slaps me in the face again. I am dreaming about him every night. I can't eat. I just want to curl up and die, tbh. He lives three miles down the road from me and I DREAD seeing him.
God, that was long. :(