Should I give my dog to a better home?

Well its starting to get Frustrating with him when I leave. If I leave to get the mail or something he will FREAK OUT, start scratching at the door, barking even if I leave a room. So like 10 Min's ago there's a baby gate at the end of the stairs because he likes to eat cat poop (why i don't know) so I walk up and he starts BARKING so loud. When its 2:00 a.m I say "No bad boy shh" he keeps doing it. I hit him on the butt go back up he keeps doing it. He does this everyday, the person before we got him abused him at 8 WEEKS what sick person would do this??! Then hes starting to bite at my other dogs neck hes going to get big because hes only 5 months and weighs about 50. So what happens when he gets older and bigger i don't want him to hurt her. Shes like the size of a Chihuahua. I walk him everyday 3 miles a day and he goes to the dog park and hes around me all day because its summer and I rarely go anywhere. I train him and everything but i don't know whats wrong. Then he will go poop when I leave to anywhere, i let him out 7 times a day, he's potty trained but he will still go. He barks at every little noise please I need options please don't say "it's your choice."