And obviously you did read my posts and I did not read yours very thoroughly...
To say that Boromir fell off the wagon in a heartbeat negates why he came to Rivendell in the first place.
He came looking for help in the defense of Gondor. He thought he was entitled to that help because only Rohan was helping in the defense of Middle Earth against Mordor.
When he saw the ring, his eyes glinted so Tolkien wrote...
To me (and everything here is opinion so there really is no right or wrong as in a test... if you believe Boromir fell off the wagon, that's fine...) Boromir came looking for help, and the moment the ring appeared and was identified as the one ring... Boromir understood it to be a weapon.
In the Two Towers, when Sam is talking to Faramir in the chapter "Window on the West", Sam says about Boromir. "I watched him from Rivendell onward and it was clear that he watched my master. In Lorien, I became convinced he would take the ring."
Also, Faramir is not surprised that Boromir made a play for the ring.
In Return of the King, when Faramir returns and Denethor finds out that he did not take the ring when he could have, Denethor said that Boromir would have brought him the ring. In fact, Denethor fully expected Boromir to bring him the ring.
And lastly, Gandalf tells Denethor that he did not trust Boromir.
So, it is my contention that Boromir planned to take the ring the whole time... to use the ring as a weapon for the defense of Gondor.