小题1:I feel lonely.
小题2:Because one of his best friends isn’t around. / Because one of his best friends moved to a different school or a different class.
小题3:The best way to make friends is to be a friend.
小题4:Because they have trouble doing this or they feel shy. /Because teachers are usually pretty good at matching up friends.
小题5:I should look for chances to say hi to them, smile and be friendly./I should be friendly/I should learn to listen to others/…