I feel so bad for all involved. It must have been a huge strain on them all for these two young couples(Corwins and Lees), who worked together (JC and CL) and were neighbors and initially friends (socializing, going to the horse ranch together) to work things out when CL and Erin were having an affair under the noses of their spouses, living next door to eachother and all. I think they were probably just trying to figure their way through it, and all four of them were just taking it one day at a time when it became apparent that the affair wasn't over and Erin was pregnant. What to do? No way of knowing what JC and NL were thinking/planning to do or trying to come up with a solution-- there just isn't any evidence either of them were taking action -- it's all rumor/speculation how wronged/angry/vengeful they felt about the situation.
What we do know (from LE affidavits justifying the search warrants) is that CL and Erin met up the day she disappeared, and they obviously talked on their way to the hunting trip/'special day' to celebrate her pregnancy. It could have been as basic as "what are we going to do? how are we going to deal with this without screwing up our current marriages/lives/careers in the USMC and having everything blow up in our faces?", i.e., they were feeling eachother out and going off for the day to talk it through.
Maybe Erin was more hopeful and excited that they could figure out a way to be together somehow, and was still enamored with him and in the throes of their love affair, but still was keeping the possibility open of staying with JC and having the baby with him (she told him she was pregnant) if it was a no-go for CL because of his obligations to his wife and daughter and his just finishing up his 6 years of service with plans to return to his home in AK, etc.
So she thought they were just going to talk it through and work things out when she went off with him willingly that day, but he already had decided there was no workable solution for him and her wanting to keep the baby and pursue the possibility of them making a life together somehow was too much of a threat to all he held 'dear', and he couldn't bring himself to dump her without there being huge repercussions for him that he would not tolerate. So he strung her along and pretended to be on the same page (let's celebrate your pregnancy) to get her alone, but it was just a ruse (hence the lying in wait charge), and he planned to and did then murder her once he got her to a remote location where he was sure he could dispose of her body and it would never be found, and his infidelity and getting her pregnant would never come out and he could go on his merry way.
I truly think it was that simple, and whether NL pressured him (or worse) and/or he was worried about losing his family/child support/demotion/finances/looking like a schmuck, etc., and/or JC and/or NL were livid and collaborated somehow to end the affair or cover things up because of their huge emotional investments in trying to right their ships and restore their relationships/status/avoid additional embarrassment, those possible contributing factors were peripheral to CL's decision to take her life to make his problems go away, because he has no conscience and is a narcissistic sociopath, just like Scott Peterson. He did it, he got caught and is charged with her murder, and he alone is going to have to face justice, and all the rest is just excuses/noise/boohoo for you. I don't care if his wife 'made him do it'. He did it. End of story. JMOO