I'm watching Season 6 and yeah, it's Luke's fault. I think after the whole shock about finding out that he had a daughter and told Liz about it. He probably thought he should forget about it until he heard what Christopher is doing for Rory and that made him feel like crap. It seems like Christopher often brings the worst in Luke in which he would become insecure and make irrational decisions involving Lorelai. When he became focused on April, he definitely became extreme oblivious to how Lorelai is feeling and I hate to say this because he's one of my favorite characters but... he became an *sshole to Lorelai.
When April's birthday party came in and he didn't want Lorelai involved. He ended up realizing he did need Lorelai's help and it turns out that Lorelai would be good in April's life since she likes Lorelai. Anna ended up making him more insecure and he just acted so stupid. Then when he decided to choose April over Lorelai. He had no idea what he was doing and when Lorelai told him she slept with Christopher. All of the bad sides of Luke started to unveil as he became convinced that he and Lorelai weren't meant to be together which was total bullsh*t.
I don't think April was at fault at all. She even wondered where was Lorelai since she really liked her and I think she knew that inside, her dad was hurting somewhere and probably even tried to get him to move on because she was concerned. She really was a positive influence on him knowing that he can be a really good dad. I think it was the moment she got sick and he found out that Lorelai married Christopher made Luke realize that it was all his fault. Here he was, sitting on his daughter's bedside, watching some old movie, and probably began to think about what had happened in all those months that led to the break-up and realized, "it's all my fault". He neglected Lorelai, he pushed her to sleep with Christopher, he made her feel like sh*t and claim that they didn't belong together, and then got her to marry that smug, Yuppie d**che. And the worst part was that he hadn't even hit rock bottom yet.
That rock bottom would be the idea of losing April just as the two were starting to really bond and have this father-daughter relationship that he didn't expect. The moment his niece was born and holding her made Luke realize he had to fight, even if it killed him. It was also clear that April needed her father because all those years of not knowing that she had a dad for so long and just having this relationship I think made Luke a better person. She also helped in his decision about his father's boat realizing that if he needed to change. He had to do it for himself to become a better person and she in many ways, did that.
People rag on April for driving Luke and Lorelai and that's way too easy. I consider her to be the unofficial fourth Gilmore Girl, w/o the name.
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