So I've never posted on this board before, but I saw you're post and thought I'd respond.
Yes he went back at the end. He stopped his boat at some weird gas station island thingy to gas up and ended up killing a really rude guy in the bathroom of the place. Then Harry finally showed back up and told Dexter that watching him kill the guy was the most human thing he'd seen Dex do since Rita died.
Dexter cried and screamed a little bit on the floor of the bathroom. The next scene jumped to the funeral and everyone was standing around waiting for him. He showed up and gave the eulogy pretty much saying how Rita made him a better person and how he should have protected her but didn't.
The End. (Hope that helps and wasn't too confusing.)