Stylistic device interpretation?

In silent nights and monogamous beds

Then you imagine what you are missing in life.

Our nerves are fraying. If only we had that,

which, because it is not there, quietly torments us.

You prepare yourself in the train of thought

what you want – and then you never get it…

You always want a big long ,

and then you get a little thickness –

C'est la vie – !

What does monogamous bedding mean?

What does the alliteration "think you" show?

What does the phrase "great length… small thickness" mean?