Jayee, if you look further in the area Character, guotes & scenes, you'll find a thread "how did Jack Die? it might answer some of your questions. then again it might not.
The second ? is a flashback that Jack is having about their first times on BBM, am sure that is discussed somewhere too, couldn't find it with a quick look, you never know how the threads are titled.
Personally, yes think that Ennis was jealous of the relative freedom Jack had or made in comparison to his - again it is discussed somewhere, probably Jack/Ennis last scene or something along that line.
Enjoy the board, you will find lost of discussion.