Hi justwanttobeme
re your comments in quote marks:-
"I agree it's not good for my DC to see but not sure if leaving is a better option".
Why do you think that?. Staying with this man is doing none of you any favours at all; he will continue to rule the roost and further teaches the children that a loveless relationship is their norm too. You also seemingly get nothing from this relationship with him, you have not answered what you get from it probably because you cannot.
"We'd have to sell the house if we separated and would be very little money left after the remaining mortgage plus some debt was paid off so unless it left enough money to place a deposit on a rented property I'd have to apply for a council property and obviously they are not easy to come by so I could potentially make me and my DC homeless. I only have a part time job so money would be very tight".
This may well be mere supposition on your part; you are married and as such have legal rights. I would seek legal advice re all of the above asap. I actually doubt very much that you would become homeless and it may well be that you could stay where you are. No obstacle to leaving is actually insurmountable, you just need to give your own self permission to leave.
"I know deep down I'm letting my DC down but I can't shake the feeling of failure for separating also. Especially when it's doesn't feel bad all the time, things can be good for weeks even months without a bad episode of him being angry or upset".
If anyone has failed her its him for treating you and these children in the ways he has and continues to do. His actions are based on and around power and control. Your second sentence here is really describing the nice/nasty cycle of abuse which is a continuous one. You're constantly awaiting the next outburst from him.
"Whilst I believe I do love him I'm not sure I'm in love with him and haven't been for many years".
Your kids have picked up on all the vibes between you two at home and have likely seen more than either of you care to realise. Do not do your bit to teach them that a loveless relationship for them will be their norm too. Do not let them ever wonder of you why you put him before them.
If you do want to be as your username suggests then you will have to separate from him.