This is most likely a rounding bug where the spawned portal in the nether, when trying to find a portal back in the over world, does the search but due to rounding and the 8 to 1 conversion rate, it will not find your original portal.
If you want a fix to this its the portal in the nether you want to destroy so that you can have it randomly generate a new one and give it a go. The problem is this means you have to hop to the nether, destroy the portal, store your gear and then die. When you go back into the nether your portal is going to be a bit of a ways away so make sure that wherever you store your gear it is -very- obvious to find it again.. Make sure you write down your coordinates and the like.
If hopping back into the portal to the over-world did not bring you to your original portal, it never will.
Please note that this rounding is potentially how to fast travel via nether hopping (hop into one portal and back out again to move 'forward' in the over-world).
Hope this helped.
The short answer is no. When You enter the a portal from the nether, on your way to the overworld, Minecraft calculates the primary portal coordinates with this generalized equation:
{X, Y, Z} → {floor(X) × 8, Y, floor(Z) × 8}
The game then checks for an active portal in a 128 block radius around that location. Given your nether portal coordinates:
X: -70; Y: 72; Z: -139
Your overworld portal must be within the following horizontal bounds:
X = -688, -432
Z = -1240, -984
Remember, any overworld portals within 1024 blocks of each other will link to the same nether portal, because 1024 blocks in the overworld = 128 blocks in the Nether, and the game checks for portals in a radius of 128 blocks.
If you build a new nether portal at the blaze farm and destroy your old portal, your main base portal will probably link up to your blaze farm. However, when you attempt to go back to the overworld, Minecraft will look for a portal within the above bounds and create a new one if it doesn't find one.
Your best option is probably to build a rail line from your current portal to the blaze farm. Ghasts can destroy any block with a blast resistance below 20.17, but they won't shoot at you without a line of sight, so you can make an inexpensive safety-tunnel around your rail line with pure Netherrack.
You can also build a more scenic tunnel with stone, glass, leaves, fences, etc, since Ghasts cannot "see" through transparent blocks.
Best Answer
As has already been said, you cannot build a portal in the End.
However, they can still be hacked in and used. Using creative mode and INVEdit, I located a naturally spawning End portal frame, and traveled to the End. From there, I placed a portal block and traveled to the Nether. Finally, I placed another portal block and was spawned back on the Overworld.
End Portal: (-1007,16,-123);
End Spawn: (100,53,0);
Nether Portal: (89,64,-21);
Nether Spawn: (11,62,-3);
Overworld Portal: (8,46,20);
Overworld Spawn: (74,64,163);
Note than when I spawned in the Nether, I was inside other blocks and no Overworld portal spawned with me. Spawning back to the overworld worked fine.