XX:很感谢你一直对我的支持!在你的支持下我会更加努力的!你为我做的一切另我感慨万分.我不知道应该如何表示我对你的感激之

XX:
Thank you for always supporting me.I'll try better under your support!
I feel deeply grateful for what you've done for me.I don't know how can I express that kind of feeling!
Please believe in me!I won't let you down.I'll be successful!
Best Wishes
Yours sincerely:
XXX
可能我不用管这样的事
不过这封信还真的很扭捏
讲英语的人最讨厌这样子的信咯
=枫's guarantee tag=

同意。不用讲一些虚无飘渺的陈腔滥调，让人看了很不舒服。还不如就写张感谢卡或是送个小礼物。
I would express my gratitute for your constant support. God bless you.
(I'll try better under your support, 不通）