I don't personally understand why you would break up with him because his wife broke up with your husband. However, I would also say that the breakup (with you husband) sounds like it was handled terribly! No reason given, you were the one being told (not even him! You don't dump someone through his wife!), etc.
I'm not sure if you should have seen it coming or not. I guess if your relationship depends on other people's relationships, it's less stable by definition, since it might break up if something goes wrong in any of the relationships rather than just in your own. It also makes it hard to fix the problem if it's a problem that's not even in your relationship.