first time back on a PC for while and wasn't going to type this out on a dang phone with all the typos that would ensue (not that I'll be any better on a computer, but meh)
so, that gap is most likely due to 1 or a multiple there off of 4 things.
1. seal isn't fitted correctly
2. striker pin is misaligned
3. hinge has been misaligned
4. hinge is bent.
how do you fix these you ask?
1. check the seal all the way round, make sure it's sitting on the flange correctly and it isn't wibbly (technical term), espeically on the door jam (where the door closes on). this is a easy thing to check, if you want to post some piccies I'm sure we can point out issues.
2. look for evidence that the pin (it's really a loop) has moved. obvious signs are defects in the paint where it used to sit. if it's moved outerwards then the door will present a gap as shown in piccy 1. given that you are also showing an off gap to the front of the door this will only be part of the issue if at all. as with 1, post some pics around the striker if you aren't sure. if it looks like it's moved, realign it to the paint markers. while you are at it, look at the lock in the door aswell as it might have been removed and refitted badly (especially if it was making the grinding noise and someones had it off to put the pin back in).
3. refer to check 2 but replace striker with hinge, I'd be looking at the upper hinge but don't ignore the lower.
4. now this is where the real skill comes in, because you won't be able to see any issues if the hinge is bent (note, not just the hinge but also the thin metal were it attaches to the piller and door return). basically, if it isn't the first 3, it's most likely this. A bodyshop or paintless dent removal place will have all sorts of fancy wedges and air bags for fixing this, so if you aren't sure, then seek proffessional help (Therapy might be a good idea too when you see the bill). In essence though, what they will do is place wedges between hinges (a block of wood will do), upper or lower depending which is out of wack, and gently close the door to move the hinge pin and mounting area around, put air bags beneath the door and lift it whilst closed, you can do this with a wedge and close the door on it slowly or manually with the door open by lifting the door. air bags to move the door for and aft, which you can't really do, but it used to be done with a pair of wedges between both hinge and slowly closing it. a no point do you want a wedge riding on the door edge, it should all be on the return and over a largish area to stop deformation.
worst case is shimming the hinge mounts, but no way would I suggest you do this yourself as it needs a really fine touch and some rather nice tools to hold the door up.
hopefully that will help you. good luck.
