Thanks a lot! see my response.

I stopped envying what I do not have, but feel grateful with what I do have.--> I stopped envying what I do not have, but felt grateful with what I do have.?

Good catch! thanks!

Upon reading Carpediem’s essay on his marriage taking away his loneliness, --> Upon reading Carpediem’s essay on how his marriage taking away his loneliness? 

Bingo! I thought about adding it while writing. This one reminds me of what I wrote for my first toastmaster visit. Remember I had something "about how my mentor doesn't feel nervous any more", you or cutestream said maybe get rid of "how".

I thought I could write something down about --> I thought I could also write something down about?

Not sure about if it is "also" here, since I am writing something different from Carpediem's.

what my marriage has brought me --> what my own merriage has brought to me?

This "to" is optional, as you can say, he brought me two apples, and also: he brought two apples to me.

I no longer mouthing along Annie Lennox’s --> I no longer mouth along Annie Lennox’s (however, not sure on the usage of "mouth along")

Good catch!

I saw this expression "mouth along" recently in A Free Life.