One reason I am able to change through therapy is the fact that my husband doesn't know I go. And since we can never change anybody else, only ourselves, in the hypothetical situation that I would want my marriage to change (not saying that I do want that, nor that I don't want it) the change would have to come from me anyway, so there is no reason whatsoever why H should be informed of my therapy. I don't think he'd be particularly interested in any case.

Here's the thing: we are not our marriages. A romantic relationship is only one aspect of life, and it doesn't have to be the most important one. If and when you grow as a person as the result of therapy, that affects you, but it doesn't necessarily have to change your marriage unless you want it to.