Louise,in all honesty your probably his cake and he is eating it
Their relationship broke down many years ago but they stay together because of the children
I wonder how many mistresses have heard that one I am not being judgemental mate but he is telling you exactly what you want to hear,marriage is broken down,only together for the kids,yadda...yadda...yadda,,,give him an ultimatum and stick to it,not 2015 or anything stupid,give him a couple of months then return and tell us your living together in bliss,but something tells me in 3...6...9....12 months he will still be with his wife and kids,brutal but an educated guess.