You've gotta do whatever you think God wants you to do, but at some point you're going to have to ask yourself why these 'marriages' keep failing.Is it wrong for me to take and marry them with them promisimg and committing to me and God?
For whatever reason, it seems built into human nature to look for sets of three ("good things happen in threes", "three strikes, you're out", celebrity deaths...), and you seem to have hit the three strikes rule. This would be a good time to sit down and try to figure out why these relationships aren't sticking and looking for what you could do to affect the outcome next time around.
There's also "fool me once, shame on you; fool me twice, shame on me", but that doesn't have a line for the guy who gets fooled three times. What are you missing that is creating this revolving door of relationships?
Put another way, how many times would this have to happen for you to consider the possibility that you're doing something fundamentally wrong? Three? Four? Eight? Ten? If you don't see a line somewhere, then it is hard to argue with your wife's assessment that this is a convenient way for you to have access to more women without sufficient regard for the long-term consequences to your two faithful wives, the women who come and go, and your own soul.