feeling let down, loneliness

I feel let down.

私は寂しさを感じます

I feel let down by my friend.

私は友達に寂しさを感じます

I feel let down by my friend at the gathering.

私は集まりで友達に寂しさを感じます

I feel let down by my friend at the gathering on my birthday.

私は自分の誕生日に集まりで友達に寂しさを感じます

I feel let down by my friend at the gathering with my younger brother on my birthday.

私は弟と自分の誕生日に集まりで友達に寂しさを感じます