I read this thread with interest as I am in a similar position, the second wife of a DH who pays up to 40% of what we bring home together to his ex despite the fact that his DC have long since grown up and moved out of home.
Why he does this? He feels he made a vow once upon a time to support his ex and they decided together that she would stay home and look after the DC.
He also feels that as he was the one who wanted out of the marriage she and the children should not have to suffer financially as a result.
All of this I have been understanding about, I know it comes with second wife territory that we work long hours with young children to effectively support two families.
Like other mnetters have said, I do admire how much he cares about providing for his family. I do accept this 'baggage', so to speak. It is a daunting thought that we will be effectively supporting his ex for the rest of her/ our days.
Often I have felt frustrated about the high expectations he seems to have of me, working, young children and keeping home etc etc... it has often felt unfair in comparison with an ex who has never worked at all.
Many times we have struggled to meet our obligations, his ex has NO idea how much stress we often endure juggling finances and managing our overall financial picture.
I have no doubt that if he was to have paid what he was legally entitled to this would have been a much much smaller sum of money than he decided to pay.
I do agree though, that at the end of the day it is never about money - it is all about the emotional motivations behind the behaviour. Whether it be pride, genuine caring or guilt - we're married to men who give far more than they need to legally.
Sorry, this is probably not all that helpful, but wanted you to know that I do understand your frustrations!! It does seem unfair - hope you can talk this out with him and will be thinking of you.