I don't have time to read everyone elses replies at the moment. Sorry if there is a repeat...
I suggest full independence from one another financially. Perhaps put a percentage of your earnings into a joint account to pay for the mortgage and any other joint assets and then the rest is yours to spend where you see fit. I do this in my marriage and it works well. It sets us up to be independent and responsible for ourselves... something that I don't understand why people don't do more often... it seems our traditional monogamous culture breeds relationships of co-dependence in all areas no?
So what to do about the past? Well, I suggest chalking it up to experience and get on a future of being more responsible financially and emotionally/communicatively (is that a word?
)... there is nothing that breeds confidence more in a partner when the one that has fucked up gets on making it right and stays on the course that is negotiated and agreed to.
If you want to help your She, then do so, but not at the expense of your financial obligation to others... now that you are aware and have figured this out, change it! She might have to get about taking care of herself more, something that she could of and should of done from the beginning. You are a kind man to help out, but you have made her obligated to you by enabling her inability to take care of herself. You now possibly feel obligated to her because you have set a president in giving her money. She expects it now and relies on it. Time to face reality that she has to take care of herself and her child. I would encourage her independence, seek your own and work on your marriage... it sounds like you are heaping a bunch of guilt on your spouse for stuff that you and her agreed to in haste. Maybe its time to take a step back, look at what you have created and make changes that will make you both happy and still strong together.