That's beautiful, Roberta. Here's my suggestion:
Throughout the years, Andrew, I’ve always been so proud of you and impressed with all the effort you’ve put into doing your best. Your hard work, dedication and patience have brought many wonderful and exciting experiences and accomplishments; you can be proud of yourself.
I've watched (I have is a more formal; I've is more intimate) you grow into a fine young man with such kindness and compassion for others that any mother would be proud of. I've been truly blessed to have a son like you.
Always believe in yourself, the way I believe in you.
Love always ~ Mom
Congratulations, you deserve all the best.
Your Brother ~ Nick
Student or Learner