I do something like this now. My girl is not the best with money and doesn't make the greatest decisions. I pay all the bills and make sure that everything is cool financially. On 1 hand, it is a bit like being the only adult in the relationship. On the other hand, I don't mind because I know that things won't get done by anybody else as well as I can do them myself. I give her spending money after all the bills are paid.
I've been trying to get her more involved in the actual responsibilities of running a house though. I told her that she needs to learn how to do these things, because if something happens to me that she would lost and in a world of trouble.