I think the relationship started on a downhill slope in late 2014, and was over , for the most part, by Feb/March of 2015 (she was into CG by then, maybe earlier). What happened, in summer of 2015, is, I believe, is that JW was comin' back round, and they may have gotten loopy together, and, since August would have been their 5th anniversary, and they'd been supposed to get married on their 5th Anniv. in Aug. 2015, I think she had a weak moment, and slept with him. Then he hopes like everything that she loves him again, that the baby is his and she'll get back together with him.
Look at CG's FB. That picture of her, on there, is one big eff you, to everyone. Then she and CG split and she just dislikes him somethin' fierce afterward. He didn't get to see K til after the paternity was established and his sis got custody of K (and R), not CG. Then HMR strikes it up with CH. Even HMR's own family isn't keen on him, so we know that CG and the Ws weren't tickled about him, but HMR tells FR it's none of their business (FB Fight after K's birth).
CH is the only guy, in pictures with S., on her FB. She tells them all via Public FB, that CH is going to be the father figure to K. Even a stranger jumps into the fray! That surely didn't go over well with JW nor his family, if it didn't go over with her own bro and sil. I don't think custody was the entire motive, but I think that it was a factor, and the final straw. You've got a lot of things going on, and then another man steps in, and he's one that not many people were happy about. I had a theory at one point that the murders were made to appear CG did it, and had an accomplice. He was being openly rooted out of his infant child's life, was the most recent male who was dumped, and was just openly disliked by HMR. What better patsy.