Shall I leave my cheating man ?

My husband of 12 yrs was my childhood sweetheart. I say was coz he is not anymore he is seeing another woman now although hhe never admits it. I have caught them red handed more than once together alone in a secluded place . We have two lovely kids who adore their father. Life was too good to be true for the first 10 yrs of marriage - he worshipped me but when i went abroad to start off our immigration process, he helped a neighbour of ours out of a bad relationship. I hung on, hoped, cried, prayed ,begged did all i could.. left everything abroad and came back for him but I think its too late... I hate to say this but I couldnt bear the pain and now I am cheating on him ... he does not know it but this man i'm with now is like a soothing balm for my aching soul.. i know i'm wrong... but my husband will just not open up to me - my guess is the other woman is threatening him - she's quite a psycho case and has tried to end her life a few times - is he a dog ? I know i'm behaving like a ***** right now as well but I dont know what else to do ?