meet.rb

def self.meets_all(user)
  Meet.where(relationship_id: user.relationship_id).order(meet_day_start: :desc)
end

current_user.parter.meets.order(meet_day_start: :desc)

user.rb
--
def partner_meets
  partner.meets.order(meet_day_start: :desc)
end

posts_controller.rb

def index
   @my_effort = current_user.efforts.order(created_at: :desc).first
   @partner = current_user.partner_user
   @partner_effort = @partner.efforts.order(created_at: :desc).first
   @posts = Post.where(user: [current_user, @partner]).order(date: :desc).page(params[:page])
end

user.rb

belongs_to :partner_user, class_name: "User", foreign_key: 'partner_user_id', optional: true
has_many :meets, dependent: :destroy
has_many :rewards, dependent: :destroy