Spoiler Yeah, he's the main villain. And as to him being an Autobot, you have to remember that above all else he's a Cybertronian; therefore he will probably do whatever is necessary for the well being of Cybertron (in his own eyes). .
Spoiler yes to both: he's the villain and an autobot . remember in ROTF in the forest battle Megatron asks Prime whether saving their entire race isn't worth a single human life? Spoiler well Sentinel doesn't follow Optimus' pov here, for him Cybertron is well worth sacrificing human live(s) although he's still an Autobot in as much as he disapproves of the Decepticon's methods to the point that hebeats Megatron into submission, taking over management of his army .
okay you want the truth here it is sentinel goes to earth in the ark to make peace with megatron (who is frozen) but starscream manages to shoot him down before he leaves cybertron so he makes it to earth but crash lands on the moon. When the autobot find him thy bring him back to wherever they're at bet then he betrays them and kill ironhide in the process he then forms an alliance with megatron and tells the world that he needs the planets resources and space bridge them to cybertron unbeknownst to them he plans to space bridge cybertron to earth to take its resources but in the process destroy earth. while during the chicago battle sentinel tells megatron he doesn't need him and pushes him off a building. MEanwhile optimus fights shockwave kills him, uses his blaster and shoots the space bridge exploding it. With the earth safe he fights sentinel and during the fight carly manages to make megatron fight sentinel too and they both defeat him with his own acid gun. then optimus and megs make peace, megatron and his decepticons go back to cybertron while optimus and the autobots stay on earth. that is what happens i know its long but thats what happens huh that is probably many many minutes of my life i will never get back
