At some point the going to be spotted by Trinity's family. How's he going to explain that?
As far as his wife, I think they're going to let it slide quite a bit due to the ongoing tragedies involving his family. I realize as a 3rd person we can see the connections as fairly obvious, but if everyone who had various connected tragedies was a serial killer then there'd be a lot more running around out there.
I guess ultimately it'll be interesting to see Dexter balance being a single dad and a serial killer. That's I line I wouldn't have ever dreamed of typing in my life. Plus if there was a possibility of them drawing connections they would have done it at the end of the season, unless they are going to drag it out through next season which would kill the shows quality over all.
Also Dexters involvement with Trinity's family could be considered coincidence as he was seen at 4 walls builds and was just a disturbed soul looking for guidance. Since he appeared as the protector of the family I don't think they would throw him under the bus and Trinity's son is probably a good candidate for protege in the next season.