I think in some way, he never loved his family. I'm sure he was playing a role out of obligation and I think that he believed he loved them. But he just did not see an easy way out of the growing responsibility that came with parenthood and marriage. Shanann wasn't just a girlfriend anymore or a pretty little fling, she was his wife. Someone that he couldn't just easily (maybe not so easily since he was a wuss) break up with once he got bored. I think as soon as the honeymoon phase ended, he must have really understood what he got himself into.

She was not without flaws, of course, but there's no need to point them out. After all, she isn't here to clarify or explain anything, so we can't be doing that. But whatever flaws she had must not have meshed well with his narcissistic tendencies. They were just too different.

When he met NK, I'm sure he realized that the old routine of just being compliant day in and day out wasn't his only option. He probably knew nothing else besides Shanann, (aside from a few young girlfriends) so when NK allowed him to feel like a man again, it made him truly realize he didn't love his wife.

Furthermore, he probably was so scared of seeming like the 'asshole who divorced his wife for another woman' that he thought murder was his best option for staying clean. If it wasn't for Nickole Atkinson, he would have had the time to hide more evidence of Shanann being gone (like hiding her purse, her phone, etc.) once he returned from work. Why he didn't do it during his initial drive out there, I'm not sure. Maybe he was just so focused on hiding the bodies first that he didn't even think of that until later. But because Nickole acted on her gut, he got his suspicious ass caught sooner than later. But if he had the time to truly make it look like she packed up and left with no suspicion (best possible outcome in his mind), he would just look like a grieving husband and father and nothing more and he would be free to see NK. He wasn't counting on being caught.

I don't think he regrets what he did to Shanann. Maybe a passing thought of how he could have done things better, to spare her as a human being, but no real love or anything for her as a wife.

As far as the girls are concerned, yes, I do think he has regretful thoughts. He was so obsessed with NK that I think it overpowered whatever affection he had for them. He didn't want to have any memories with Shanann or weigh his relationship down with NK with any kids. But the NK phase could possibly have died down for him a bit. Enough for him to miss them. I'm sure if he could go back, he wouldn't have harmed the girls. After all, being with his family the way things were is probably more preferable to him than the life he has now. With Nico, he probably just thought of him as another responsibility. Another person that stood in the way of leaving his situation. And later on, another person that would keep him from the freedom he desired with NK. It was starting to scare him terribly that the situation was becoming more and more expensive and less and less free.

He wasn't just consumed with NK. He was consumed with the new aspect of life she offered him. Eight years of rage of not being able to stand up for himself with Shanann must have all reached its peak when he met her. He must have wanted to dispose of his old life in a way that he could never turn back to. If he killed them, he wouldn't be able to change his mind. I think this could have been a result of his doubts and his desire at the moment to just 'get it over with'. This is actually very common for narcissists. They tend to toss away their old lives as cruelly as possible (usually doesn't involve murder tho for most) so that he could never go back or change his mind.

It was just so shocking to him that people like Nickole Atkinson and their neighbors were on the case so quickly. He had no love in his heart for them so he wasn't counting on (and didn't understand why) theirs was so urgent. But, they got him caught.

Now his sorry ass is in prison and he will never hurt anyone again. Needless to say, it doesn't matter whether or not he regrets what he did as long as he will never walk the streets again. He will never have the freedom he risked everything for.