1. at the same -> is at the same

2. get upset ->  feel upset

3. Also ->  Moreover

Dear Jay,

Thank you for inviting me to your farewell party. I know that you really want me to take part in it. But I regret deeply that I cannot attend your party. I've just known that my cousin's wedding at the same day as your party. I'm really confused about whether to go to my cousin's wedding or to attend your farewell party. But I am a responsible family member, I finally decided to come to the wedding. I wish that you don't -> " didn't "get upset. At the end of the letter, I want to say that I really had a great time when we studied together.

Also, I hope you will become a good student even though we don't study together.

Sincerely yours,

Jennifer