I can't tell you how many times I have heard people in difficult marriages say the exact same thing:
"I think I married the wrong person."
It's proof that our culture has embraced the lie that somewhere out there is a "soul-mate" that God made just for them to make them blissfully happy for life. Most of the people I hear talking about marrying the wrong person are Christ-followers, so the church is not free of this thinking. In fact, I think it's in the church even worse than the world.
Why? Perhaps it's because we assume that God's mission in life is to make us happy and comfortable.
Forget the commands of God about commitment and fidelity and even of enduring difficult times (even in marriage). Forget the clear directives of God about what we must DO to build a strong marriage. Forget that God's goal is His own glory and not our happiness.
Instead, our focus tends to land solely upon this: "God's desire is for me to be happy, so joy in my marriage should be effortless. If things are difficult, I must have missed God's will in marrying this bonehead. The only way for me to get back into God's will is to dump this wrong guy and go find the right one." Of course, this requires us to disobey God's will (divorce) to find God's will (our soul-mate). It's crazy.
Please note: I believe God is sovereign in all things, so yes, that means that He foreknew who you were going to marry. And if that's true, then it means He predestined who you were to marry. (My head hurts when I try to process these things.) However, that's God's perspective, not yours. You are not God and therefore don't have the luxury of trying to decide who "God's man or woman for you is." Your responsibility is to obey what He gives you in His Word.
Here's what you CAN know: the one you married is the one you married. And it's likely that, from your perspective, you sometimes feel like you married the wrong one. But God is with you and He desires to show you how only He can redeem even the most difficult of circumstances.
If you're concerned that you and your spouse aren't compatible, then welcome to the club. I have encountered very few couples who could honestly say that they were fully compatible with one another. In fact, many smart people are now saying that compatibility is a myth. (None of these people are named Neil Clark Warren.)
There's a brief excerpt from Timothy Keller's new book "The Meaning of Marriage" that covers this topic quite nicely. You can read it here: You Never Marry the Right Person. He's a smart guy. You should listen to him.