Cheating is a trigger for me, and brings up lots of issues for me. The way Seth handled the breakup at the end really hit home for me in a painful way.... I think I'm going to have to take a break before reading the next book. I need to not be so attached when I read the painful stuff :P
Other than the end, though, I really enjoyed the book. This was the first time that I hadn't figured out the mysteries at the beginning of the story.. so that was cool to see them unfold.