Answer:
Dear [Relative],
I hope this letter finds you well. I wanted to reach out and express my disappointment that you were unable to make it to our recent family celebration. We all missed you and your presence was definitely felt.
I understand that things come up and plans change, but it would have been nice to have you there to share in the joy and memories with the rest of the family. From the delicious food, to the fun games, to the heartfelt speeches, there were so many special moments that would have been even more meaningful with you there.
I want to let you know that we all love and care for you deeply and hope to have you with us for our next gathering. Please let us know if there is anything we can do to help make that happen.
Warm regards,
[Your Name]