And he didn't even learn about that until much later, lol.
And he held that belief with Ben as well. But one slight single moment of doubt that faded as fast as it appeared was enough to push Ben over the edge.
As far as losing faith goes, everything he did in the Original Trilogy built up his faith. Vader's turn proved he was right that the light side would prevail, and Palpatine was defeated. Fast forward, and as Luke learns more and more about the Jedi Order of old, small seedlings of doubt creep in. The light side may always prevail, but were the Jedi really all they were cracked up to be? If it hadn't been for some of their rules and hubris, Palpatine wouldn't have been able to rise in the first place. They're as much to blame for the creation of the Empire as Sidious or Vader are.
But, Luke has the chance to start fresh. He has his own order, his own school. He can do things right. Make a new Jedi Order that lives up to the legend. Until Ben. That swirling cloud of conflicted allegiances could plunge the galaxy into a new era of darkness. A very human mistake is made for a split second, and that future is set. Ben Solo is now Kylo Ren. The New Jedi Order is destroyed. Luke is all that remains. Again. The First Order begins it's march across the galaxy, and for the second time in less than sixty years, the Jedi have unwittingly created the oppression that threatens everyone, when they were supposed to be the safeguards against it.
Luke doesn't so much lose his faith in the Light Side of the Force as he does himself and the Jedi. If he had no faith in the Force at all, he wouldn't have ever agreed to train Rey. And whose to say he still doesn't believe that there isn't any light left in Ben? He stated that activating that saber was a mistake born of reflex and instinct, and that he instantly regretted it. Ben might have fallen to the Dark Side in that moment, but that doesn't mean Luke doesn't believe there isn't still good in him.
Even as he "faces down" the entire First Order on Crait, the only person Luke blames for Kylo's actions is himself. Luke sees himself and the Jedi ways as the problem, hence the solitude.
The bombs are able to "drop" through space because they are magnetically drawn toward their targets.
Source: The Last Jedi visual dictionary written by Pablo Hidalgo, and hence canon.
Wookiepedia would like to have a word with you...
"Hyperspace was an alternate dimension that could only be reached by traveling at or faster than the speed of light."
Argue about whether or not you'd be able to hit something whilst doing this, fine, but it is faster than light travel.