QUESTIONS I HAVE ABOUT THE HULK/BRUCE BANNER

Having only seen the Edward Norton hulk and the two avengers, and having never read the comics
  1. Didn't he have a girlfriend when he was Edward Norton?
    I get he left her to keep her safe but without any thought or mention of her he's suddenly all into Black Widow? That other woman was just as willing as black widow to put up with his hulkiness. And she never tried to contact him again once he resurfaced in avengers 1?
  2. Does he age?
    They claim that he's invincible, but is he also invincible to the effects of time? Or will he die of old age, or will he live forever but just keep getting older until he's a really saggy old man and I big strong hulk or a really saggy old man and a really saggy old hulk?
  3. Is the hulk a separate person?
    They always refer to him as "the other guy", and Bruce seems to have no control over the hulk (or dies he?), and in avengers they claim that the hulk saved Bruce from dying of gamma radiation, so is the hulk a second personality sharing a brain with Bruce? It seems pretty convenient that both hulk and Bruce have the same taste in women. What if Bruce was into one person and hulk was into another? What if hulk was gay?
  4. If they are two separate people, can they talk to each other?
    Say they both were dating two different people, could they talk to one another and work out a schedule? Bruce sees Black Widow on Wednesdays, and hulk sees Penny on Thursdays?
  5. Is Bruce immortal too?
    Mark Ruffalo claimed that shooting himself in the head only brought out the hulk, so there's no way to kill Bruce? Is his skin bullet proof when he's human? Or would the bullet break his skin and then he would hulk out and the skin would repair itself?
  6. How does the hulk go away?
    I get that Black Widow can calm him down, but is calming down what it takes to go back to Bruce? In the avengers 1, he falls from the sky as hulk and when he wakes up, he's Bruce, so I thought sustaining a major injury just turned him into Bruce, but that didn't seem to be true in any other battle ever.
  7. Does hulk grow more facial hair when he hulks out?
    Like if Bruce had a beard and he went into hulk mode, would he grow more hair to compensate? Or would he just have the same amount of hairs with them all awkwardly spaced apart?
  8. Is Bruce a scientist or a medical doctor?
    They always remind us that he's a brilliant scientist who can make a bunch of stuff, but is he also a medical doctor? Because that's what he was doing in avengers 1, and I feel like he wasn't really qualified for that work.
  9. Why did he leave after avengers 2?
    Why did hulk see his girlfriend and then decide to just shut her out and fly a ship until it crashed? Did Bruce decide that or did hulk? And hulk seemed pretty calm there in that scene, why didn't he change back to Bruce?