Answer:
Dear .........,
I hope you are well in your new boarding school and you have made new friends. I miss you and all the conversations we had during our school days. However, I must share with you that my mom had become my best friend since you left. She always listens to me and gives me care and support. Though she has always been very affectionate, now she goes out of the way to take care of me.
We have become the best plans. I share the minutest of details with her. She knows all my secrets and now she is also aware of all the pranks that both of us have played. She made me understand that a few of the pranks could have had adverse effects and I should not repeat them. I confide in her for everything and I trust her completely. I look forward to seeing you during the next vacation. I would love to introduce you to my sister and all three of us can have a great time together.
Till we meet next, I will look forward to see you soon.
Wishing you all the best in all.