it is hard seperating the relationship and the dc - it is a package afterall.
Your comment about something being broken and not being able to be re-paired sounds how i have felt in the past.
After his cheating did you not consider your old relationship dead?
I think that is what i had to do.
As for him making you happy - he cannot - you have to find happiness yourself.
I think you need to take a look at what you want now and i know how confusing and hard that it, it will change over time and with life going on it is hard to see the bigger picture.
Can you find small things you can change to make you happier - a regular night out say just for you?
Do you feel he has moved on and if you continue to mention that you are not happy it will upset him further? Because again i think i have been there - you need to sit and talk with him and it may take a very long time (but so what this is all your futures and happiness).
I really wish you luck - it is not easy staying and feeling as if you have the bum deal, but you can turn it around if that is what you truely want.
You cannot change what happened but you can change how you see it as destroying something.
For me it has opened up a lot of other possibilities for me. I certtainly will not worry about what my h will say if I WANT to do something now. My happiness does not depend on him approving what i do.
Luckily my h has been terrific and actually supports me in a lot of what i want to do anyway. He is far more willing to stay in with the children whilst i go out and we have both been brave and left the children with a nanny whilst we go away and re-build us (it feel selfish at first but actually it is not).
But i really feel for you and hope you find the strengh to do what is right for you.