Who is the losing pitcher? I need help

Well I was posed a question today that I had no idea about so I hope you guys may be able to help me.

Here is the situation.
The starting pitched goes out for the last inning and eventually gets pulled as the batting team starts to rally.
The relief pitcher comes in and proceeds to blow the game. The winning run was a guy that he pitched to. In a normal circumstance it would make him the loser but I'm unsure since the batter that scored that winning run reached on a fielders choice.

So does the fact that this batter got on by a fielders choice revert the loss back to the starter? Or is it still the relief pitchers loss?

Hopefully that all makes sense. If it doesn't I can hopefully straighten it out if you ask.
I wait with anticipation to hear what you guys say.

Not sure i followed all of that, but I'm pretty sure the RP gets the loss, as long as the runner was his

I think the SP gets the loss. From the rulebook:

10.18(g) "When pitchers are changed during an inning, the relief pitcher shall not be charged with any run (earned or unearned) scored by a runner who was on base at the time he entered the game, nor for runs scored by any runner who reaches base on a fielder's choice which puts out a runner left on base by the preceding pitcher."

10.19(e) "Regardless of how many innings the first pitcher has pitched, he shall be charged with the loss of the game if he is replaced when his team is behind in the score, or falls behind because of runs charged to him after he is replaced, and his team thereafter fails either to tie the score or gain the lead."

The SP would be charged with the run so should get the L.

You are probably right. I defer to the person who reads the rules