[The Might]

Well, I'm back from vacation to annoy you all again...
So let me try...what about Gollum?

I'm living in a land
where enchanted stream flows,
where flowers blossom, and
no fight is there, no foes. - was living with the Stoors near the Gladden

When all my work is done
uphill I sometimes walk
to visit my best friend
to simply sit and talk. - to the Ring he had in the mountains

But when darkness comes down
When lightnings fill the sky
I leave my home and town
When foe is passing by - the storm in the Hobbit; home could refer to his rock in the lake, and town could be Goblin-town, where he went to find some food; he left both as Bilbo, his foe, came.

I'm living in a land
Where cold stone serves for bed - his rock in the Misty Mountains, and also Mordor
All things will come to end
Tomorrow, I'll be dead - He could be saying the riddle while in Mordor before reaching the Sammath Naur.