I am late to the conversation, and perhaps overstepping my bounds, but I won't tell you to seek a different forum, at least not until I have some understanding of what's going on.
The problem that you have with this other woman: Is the problem that you suspect this other woman will take your husband away from you, and have him all to herself? Perhaps this is a "cowgirl" situation? If so, how can you tell that she is bent on taking your husband away?
You mentioned that she was "everything your husband wanted in a woman," and you feared that she was a "better catch than you," and that he would therefore leave you in order to be with her all the time.
Is it possible that some kind of self-insecurity is driving your fears? What can your husband do to reassure you (apart from leaving the other woman)?
Just seeing if I can get to the bottom of the rather perplexing problem.
Love means never having to say, "Put down that meat cleaver!"