Mama, he doesn't have to choose between you and her -- he can have you both. Trying to be better than her won't accomplish anything.
Quote: I do loving things for him without expecting anything in return.
You aren't going to get anything in return, because he can have his cake and eat it too.
Quote: I love him and our life and family so much that I don't want to disrupt it. It is not in my nature to be mean.
Demanding that he respect the sanctity of your marriage is not "mean" -- not by a long shot. He has already disrupted the family ... the only question is: what are you going to do about it?
"Loving" someone so much that he can treat you however he wants isn't love, it's co-dependency. Is what is happening right now good for your family? Is everyone as happy and well-adjusted right now as they were before his affair? I imagine not. So, if you really love your family, you'll take action to try to improve it.
Quote: Unfortunately, our finances are such that it would be impossible for either one of us to leave.
No, actually this is a huge advantage for you. My W can't afford to leave either. The financial pressure of living on her own is one reason that she was sobbing last night to me about how depressed and stressed she is right now and why she said she's going to try to end it with the OM. Unless life for your H becomes uncomfortable in some respect, there is no reason for his actions to change.
Surely, you could take the kids and move in with someone in your family for a while. Or if the house/apartment is in your name, just change the locks. Or borrow some money from your family so that you can get a legal separation so that you can have the house/apartment and he can pay child support -- from what you wrote, they would probably help you pay for a lawyer.
Mama, what is your plan? If your plan is to do nothing, then nothing will change.
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)