Thank you for your honesty, and also for your concern. Perhaps others who read this have been alienated from a brother or sister, or even a parent or child, and your letter will encourage them to take the first step.
First steps are hard, however, because they often mean we have to swallow our pride and admit our own failures. They also are hard because we may need to forgive the other person for what they did to us and forgiveness isn't easy, especially when we've been deeply hurt. Or again, we may be afraid to take the first step because we've been hurt enough in the past, and we fear we'll meet with rejection and hurt once again.
If we never make the effort, however, we'll never know what the outcome might have been and (as you've discovered) eventually it will be too late. But we also need to make the effort because God doesn't want us to be ruled by anger or bitterness or pride or an unforgiving spirit. The Bible says, "If it is possible, as far as it depends on you, live at peace with everyone" (Romans 12:18).
Ask God to forgive you for the past not just for this failure, but for all your sins. Then ask Christ to fill you with His love, so you can share His love with others.