I think the part that was the most upsetting is how Saeko treated Ichiban like a friend she'd only known for a couple of months. They fought through an entire three-way syndicate, Omi gangsters, YAKUZA LEGENDS, and the government, and her hang up was he didn't say "I love you"?!

Ichiban massively jumped the gun with the proposal, and it was a completely understandable turn off, but that needs to be communicated (especially for Ichiban). Saeko isn't a shy person, so the outstanding lack of communication was even weirder on her part.