Walt explained to Gus why he was so attached to Pinkman in season 2, episode 11:
Prior to his cancer diagnosis Walt didn't have a backbone....how suddenly he has a guy that'll do literally
anything for him, including murder. It's a powerful thing.
Even in season 5B, when it's obvious he's lost control of Jesse....it's obvious to everyone
except Walt. When he finally realizes, is when Walt tried to have him killed.
As far as Gus, and the meeting, Walt requested it. Gus could've refused, but
at that point he was trying to keep Walt happy.
Lastly, and this is open to opinion....it wasn't necessarily Jesse that started the dominoes falling with Fring. In season 2 Walt told Jesse to expand into new areas after word spread that Jesse killed someone with an ATM, remember? Jesse was against it....Walt convinced him it was a good idea, which is why Combo got killed, which led to Jesse wanting to kill Gus's guys.
Fred.