The entire Cordelia and Chrom situation.
Chrom: "Cameron, you're married, you must know what you're doing. Help."
Cameron: "Chrom, Anna did all the work in this relationship." <beat> "...err, what exactly is the problem?"
Chrom: "Cordelia came out of nowhere and said she was in love with me. She then ran off crying."
Robin: <blinks> "Wait, this was new to you? Chrom, the entire army knew. Literally! We all thought you just didn't want to let her down!"
Chrom: <dawning horror in his eyes> "...how long has this been going on?"
Cameron: "I'd estimate even before you caught her falling, although that didn't help matters. <groans, rubs his temples> "...dear lord. I think it's been a few years?"
Robin: "That's what Frederick told me."
Chrom: "FREDERICK knew and he never told me?"
Cameron: "...it was really obvious. Like, we honestly had no clue you didn't know."
<Chrom slumps backwards into a chair>