I thought Kieth did not understand Lois much because he was a very religious person and Lois was not that much religious. Lois thought the atmosphere and people at Benediction were not natural. I think she was stressed being at Benediction, so she saw something in the candles.
When Kieth and Lois had a conversation after praying at Benediction, Lois did not say much, only Kieth said a lot about his religion. Lois said about some intelligent people don't believe Christinanity and birth control, but kieth did not respond much about these things. He just said how faith is important for him and her.
When he said to Lois "I want you to pray for me sometimes, Lois. I think your paryers would be about what I need. Because we've come very close in these few hours, I think." Lois responded "Oh we have, we have!" She cried. "I feel closer to you now than to any one in the world." I think she felt more apart from Kieth than before. I feel her response for him was kind of hurry because she did not agree with Kieth. He did not listen Lois and tried to push his belief on her.
I think the reason why Lois decided to leave Kieth was that he did not understnad her. She wrote we can't marry and we can't lose each otehr and let all this glorious love end in nothing. She maybe still loves Kieth, but she thought she cannot live with him all her life because he does not understnad her.
Kieth and Louis knew each other for very long time, but they had different lives. Kieth had snap-shots of her but I think Louis was not a girl what he thought. She lived in Europe and had different experiences. Nobody can understnad people from snap-shots. Kieth thought he knows her very well. In fact, he knew almost nothing about her.