Jesus repeatedly promises that our prayers will be answered, but I've prayed for a loved one unsuccessfully for many years. My faith is severely shaken. What am I doing wrong? 

You're not alone in your frustrations. While I cannot provide definitive answers for you specifically, I'll try to identify pertinent truths to be considered when wrestling with perceived unanswered prayers.

PRAYER PROMISES

You mention how Jesus repeatedly promises to answer the prayers of his people. How true! "I will do whatever you ask in my name. You may ask me for anything in my name, and I will do it. . . . If you remain in me and my words remain in you, ask whatever you wish, and it will be given you. . . . My Father will give you whatever you ask in my name. . . . Ask and you will receive, and your joy will be complete" (John 14:13,14; 15:7; 16:23,24).

There is a twofold assumption here. The first is that we are praying in Christ's name and according to God's will. The second is that the Lord will answer our petitions affirmatively.

PRAYER PROBLEMS

Problems of "unanswered prayer" are real and won't go away. We may minimize or pretend the problem doesn't exist, but it persists. We are tempted to blame God, question our faith, or see our prayers as defective. Too often people stop praying rather than resorting to a healthy self-appraisal or optimistically becoming more persistent in prayer.

At times—and this may or may not be true of you—there might be identifiable reasons why God doesn't answer a specific prayer at a specific time. Maybe we don't really believe God will answer it (James 1:6-8). Perhaps we ask with wrong motives (James 4:3). Maybe we're tolerating sin, so that God won't hear (Isaiah 59:1,2; Psalm 66:18). Possibly we don't answer those who cry to us for help (Proverbs 21:13). This calls for self-appraisal.

Additionally, we do well to remember that God reserves the right to answer "No!" or even "Wait!" or "Not yet!" But all along he is answering our prayers. God may seem not to fulfill his revealed promises connected to prayer, yet God sees things differently than we do. He is all-knowing and always wants what is best for us and for our loved ones (Romans 8:28). Sometimes God allows us to grasp why he seems to deny some prayers, but many times he doesn't. That's why we're so often frustrated.

PRAYER PERSISTENCE

"We live by faith, not by sight" (2 Corinthians 5:7) is a good description of the Christian life and perhaps especially our prayer lives. Our faith knows God is one hundred percent faithful to his promises, but we don't always see that. We know our prayers are being answered because God invites prayers and promises to hear and answer them. That is to "live by faith." The ability to be content with this is a gift of the Holy Spirit.