I downloaded my WhatsApp chat history with my then long-distance fiancee (now my wife), and created a bunch of graphs and analysis. Everything from word clouds to regression to anomalies (eg when she visited or I visited, chat frequency dropped dramatically, etc).
Pretty much a Python notebook. Well one thing I remember was usage of the word "love". After we said it in real-life, there was a huge spike in usage in the chat. But the interesting thing is that even before we said it directly (eg "I love you" ), there was a build up of indirect usage (like "I love spending time with you").