How do we know if we're doing God's will? How do we know if the decisions we make are the right ones, the ones God wants us to make? How many decisions have we made thinking we're doing God's will only to find out later that maybe they weren't after all?
I know someone who always wanted a cabin in the woods. When he got to the point in his life where he had the money to have one, he prayed and felt he was doing God's will by building one of his own. As he got into the middle of building (which took three years) several unexpected events happened. By the time the expensive cabin was finished he was ready to sell it. He rarely got to use it and found it was a monetary burden. He was finally able to sell it at a loss. Did he hear from God? Probably not, but he heard from his own heart.
I know of several times in my own life I thought I was hearing from God. As I looked back on those times that didn't go well, I realized I was hearing my own desires. Made me pretty mad when I realized that because I thought God had betrayed me by letting me walk into something He didn't want. I told Him how I felt. You'd expect Him, if He were like us, to say, "Well, you got into it on your own because that's what you wanted. Now get over it!" But he didn't. He lovingly showed me my heart. Then He told me He'd never left me nor forsaken me through it. That changed my life.
Paul tells us in Romans that God causes everything to work together for the good of those who love God and are called according to His purpose for them. What it comes down to is trust and faith. Faith that no matter what happens God will work it out for us. We don't know what is going to happen tomorrow. All we have is today and the knowledge that when we mess up, we can trust God to turn our lives around and fix whatever we break.
Remember--His mercies endure forever.