I receive many letters like yours because, unfortunately, many people seem to be on a spiritual roller coaster in their relationship with God. But God doesn't want our relationship with Him to be like this, and He has provided us with everything we need to grow closer to Him every day.
Let me use an illustration to explain this. Elsewhere in your letter, you mention that you are happily married. Have you ever asked yourself why your relationship with your wife is so stable and fulfilling? One reason, I suspect, is because you take time to be together, talking and listening to each other and in general just enjoying each other's company. If you never took time to be with each other, your love would almost certainly fade. The same is true with God. God loves us and wants us to spend time with Him every day. When we do, our relationship with Him will grow stronger. Take time to read and meditate on God's Word, the Bible, and take time to pray, as well. A daily time alone with God–even if it's only a few minutes at first–is the secret of a stable, fulfilling Christian life.
Make your prayer that of the Psalmist: "O God, you are my God, earnestly I seek you; my soul thirsts for you" (Psalm 63:1). Then set aside time to be alone with Christ every day and your relationship with Him will grow.