No, nothing is wrong with you; your caution is completely understandable. In fact, I wish more young people were as cautious as you have been; far too many rush into marriage without ever giving much thought to it - and the results are often disastrous.
But God didn't intend for it to be this way. God gave marriage to us - and He meant for it to be a lifelong relationship that brings happiness and security to our lives. The Bible tells us that "The Lord God said, 'It is not good for the man to be alone. I will make a helper (or companion) suitable for him.' ... Then the Lord God made a woman ... and he brought her to the man" (Genesis 2:18, 22).
Ask God to guide you in this all-important area of your life. He loves you, and He doesn't want you to experience the heartache your sister has experienced. Begin by opening your heart to Christ and making Him the foundation of your life. Then seek His will for your future - including leading you to the person of His choice if it is His will for you to marry.
Then ask Him to help you be a thoughtful and loving spouse when that time comes, and to make Christ the center of your marriage. Don't be satisfied with anything less than God's will for your life - both for your marriage, and in everything else.