So by now we know Optimus Prime loses faith in humans. However would that cause all the autobots to do so? At the end of DOTM we have 8 autobots left (Optimus, Ratchet, Sideswipe, Dino, leadfoot, topspin, roadbuster and bumblebee) Optimus we know loses faith in us. Ratchet is one of Optimus Primes oldest friend which may cause him to lose faith too and let's not forget he wanted to leave in ROTF. We still don't know if sideswipe and Dino are returning but they may be killed off so we may never know if they lost faith in humans. From the wreckers we only know that Leadfoot may return but the wreckers didn't really seem to like Humans in DOTM. So leadfoot may not really care about having faith in humans but we did see him with the 67 camaro which brings us to the last autobot Bumblebee. Bumblebee has always been the autobot closer to the humans so I couldn't see him losing faith. Bee could actually be trying to restore an alliance with humans with the help from leadfoot or other autobots. So how do you gain the humans "trust"? Well you give them something they always wanted. Since ROTF humans have wanted transformers to share their technology with them but Optimus didn't because we would use it for war. So maybe Bee shares their technology with humans (Joshua) which helps them build Stinger. Of course once stinger is built the humans use it to show how weak Bee is. So basically Bee is humiliated and betrayed which leads him to begin to not trust humans so easily until he meets Cade, Shane and Tessa.