lila was the perfect match for him

She set fire to his place when Astor and Cody were there. I believe that was his reason (unless I forgot something else).

Lila was toxic and was an absolutely despicable person even moreso than Hannah.

Lumen was a great match for Dexter but in the end it made sense for her to move on.

Yeah, I know Lila was just a baaaad case of crazy and kinda dangerous for Dex, but I thought they really were a good match for eachother. If they wanted to stay true to the concept of Dexter being a sociopath ( which they kinda just forget about in later seasons in an attempt to make him more likable , I guess... ) , they would've had him stay with Lila even after all the *beep* she did to try and kill the kids and all. Or, in an even more sociopathic manner, have him stay with Lila and Rita at the same time behind both of their backs, lol

Debra was also a great match for Dexter.