Dear LiTao
I am sorry to hear that you have some pronlems with your classmates.As you felt that your classmates are not friendly to you as they were in the past,here i would like to give you some suggestions.
To begin with,finding out your own problems.Have you done something wrong recently?Did you hurt anybody in the class?Sometimes we did harm to other without notice.Therefore,please first check your own problems.Second,communicating more with classmates.Although they did not invite you to some class activities,you still should have words with them and know about their feelings toward you.Maybe you will find out what's wrong with your relations by communicating with them heart to heart.
Yours Truly,
Wang Jin.