I'm in the camp where I don't believe any of this was due to a custody issue. People in a relationship who are progressing to marriage don't have custody issues. But then I also don't buy the "break up" story either, since PF is the only one who said they had ended the relationship, and by the way PF backtracked that statement through his attorney when it made him a viable POI. PF used the break up story because he knew it would justify his cold behavior, having his daughter for an extended period, and the last minute trip he claimed Kelsey took. As soon as it also gave credence to a murder, he changed and had his attorney state that the relationship was fine.
Kelsey was 29 years old, living on her own, with a child out of wedlock, there was no reason to paint a pretty picture for her mother in regards to the relationship she had with PF. If they had broken up she would have told her mother. So I don't think this had anything to do with custody issues.
I had thought there might be another woman, but if that were the case I would have expected that woman to come forward and given that Patrick wasn't married to Kelsey, it would be easy enough to dump her and move on. So that can't be it.
That he planned this for months says it wasn't an act of rage, it was something he mulled over which means it's deeper than he was triggered by something one day. He may have anger issues, but this was planned, done in cool moments where he'd wasn't in a heated state.
I keep coming back to it being about the lies he's told. I believe he lied to Kelsey about who and what he was. I believe he lied to his family about Kelsey and who she was. I think all those lies were catching up and it was getting to hard to juggle all the balls. I also believe he didn't want to marry Kelsey, I think they had planned a wedding and he gave her the financial excuse as a way to get out of it. He may have run out of excuses to not get married and didn't want to admit he had never planned to marry her. Sadly it may be as simple as that, he didn't want to get married and had run out of excuses. JMO